CPR assist device with pressure bladder feedback

ABSTRACT

A resuscitation device for automatic compression of a victim&#39;s chest using a compression belt which exerts force evenly over the entire thoracic cavity. The belt is constricted and relaxed through a motorized spool assembly that repeatedly tightens the belt and relaxes the belt to provide repeated and rapid chest compression.

FIELD OF THE INVENTION

This invention relates to emergency medical devices and methods and theresuscitation of cardiac arrest patients.

BACKGROUND OF THE INVENTION

Cardiopulmonary resuscitation (CPR) is a well known and valuable methodof first aid. CPR is used to resuscitate people who have suffered fromcardiac arrest after heart attack, electric shock, chest injury and manyother causes. During cardiac arrest, the heart stops pumping blood, anda person suffering cardiac arrest will soon suffer brain damage fromlack of blood supply to the brain. Thus, CPR requires repetitive chestcompression to squeeze the heart and the thoracic cavity to pump bloodthrough the body. Very often, the patient is not breathing, and mouth tomouth artificial respiration or a bag valve mask is used to supply airto the lungs while the chest compression pumps blood through the body.

It has been widely noted that CPR and chest compression can save cardiacarrest patients, especially when applied immediately after cardiacarrest. Chest compression requires that the person providing chestcompression repetitively push down on the sternum of the patient at 80to 100 compressions per minute. CPR and closed chest compression can beused anywhere, wherever the cardiac arrest patient is stricken. In thefield, away from the hospital, it may be accomplished by ill-trainedbystanders or highly trained paramedics and ambulance personnel.

When a first aid provider performs chest compression effectively, bloodflow in the body is typically about 25 to 30% of normal blood flow. Thisis enough blood flow to prevent brain damage. However, when chestcompression is required for long periods of time, it is difficult if notimpossible to maintain adequate compression of the heart and rib cage.Even experienced paramedics cannot maintain adequate chest compressionfor more than a few minutes. Hightower, et al., Decay In Quality OfChest Compressions Over Time, 26 Ann. Emerg. Med. 300 (September 1995).Thus, long periods of CPR, when required, are not often successful atsustaining or reviving the patient. At the same time, it appears that,if chest compression could be adequately maintained, cardiac arrestvictims could be sustained for extended periods of time. Occasionalreports of extended CPR efforts (45 to 90 minutes) have been reported,with the victims eventually being saved by coronary bypass surgery. SeeTovar, et al., Successful Myocardial Revascularization and NeurologicRecovery, 22 Texas Heart J. 271 (1995).

In efforts to provide better blood flow and increase the effectivenessof bystander resuscitation efforts, modifications of the basic CPRprocedure have been proposed and used. Of primary concern in relation tothe devices and methods set forth below are the various mechanicaldevices proposed for use in main operative activity of CPR, namelyrepetitive compression of the thoracic cavity.

The device shown in Barkolow, Cardiopulmonary Resuscitator Massager Pad,U.S. Pat. No. 4,570,615 (Feb. 18, 1986), the commercially availableThumper device, and other such devices, provide continuous automaticclosed chest compression. Barkolow and others provide a piston which isplaced over the chest cavity and supported by an arrangement of beams.The piston is placed over the sternum of a patient and set to repeatedlypush downward on the chest under pneumatic power. The patient must firstbe installed into the device, and the height and stroke length of thepiston must be adjusted for the patient before use, leading to delay inchest compression. Other analogous devices provide for hand operatedpiston action on the sternum. Everette, External Cardiac CompressionDevice, U.S. Pat. No. 5,257,619 (Nov. 2, 1993), for example, provides asimple chest pad mounted on a pivoting arm supported over a patient,which can be used to compress the chest by pushing down on the pivotingarm. These devices are not clinically more successful than manual chestcompression. See Taylor, et al., External Cardiac Compression, ARandomized Comparison of Mechanical and Manual Techniques, 240 JAMA 644(August 1978).

Other devices for mechanical compression of the chest provide acompressing piston which is secured in place over the sternum via vestsor straps around the chest. Woudenberg, Cardiopulmonary Resuscitator,U.S. Pat. No. 4,664,098 (May 12, 1987) shows such a device which ispowered with an air cylinder. Waide, et al., External Cardiac MassageDevice, U.S. Pat. No. 5,399,148 (Mar. 21, 1995) shows another suchdevice which is manually operated. In another variation of such devices,a vest or belt designed for placement around the chest is provided withpneumatic bladders which are filled to exert compressive forces on thechest. Scarberry, Apparatus for Application of Pressure to a Human Body,U.S. Pat. No. 5,222,478 (Jun. 29, 1993), and Halperin, CardiopulmonaryResuscitation and Assisted Circulation System, U.S. Pat. No. 4,928,674(May 29, 1990), show examples of such devices. Lach, et al.,Resuscitation Method and Apparatus, U.S. Pat. No. 4,770,164 (Sep. 13,1988), proposed compression of the chest with wide band and chocks oneither side of the back, applying a side-to-side clasping action on thechest to compress the chest.

Several operating parameters are required for a successful resuscitationdevice. Chest compression must be accomplished vigorously if it is to beeffective because very little of the effort exerted in chest compressionactually compresses the heart and large arteries of the thorax and mostof the effort goes into deforming the chest and rib cage. The forceneeded to provide effective chest compression, however, creates risk ofother injuries. It is well known that placement of the hands over thesternum is required to avoid puncture of the heart during CPR. See Jonesand Fletter, Complications After Cardiopulmonary Resuscitation, 12 Am.J. Emerg. Med. 687 (November 1994), which indicates that lacerations ofthe heart, coronary arteries, aortic aneurysm and rupture, fracturedribs, lung herniation, stomach and liver lacerations have been caused byCPR. Thus the risk of injury attendant to chest compression is high, andclearly may reduce the chances of survival of the patient vis-à-vis aresuscitation technique that could avoid those injuries. Further, chestcompression will be completely ineffective for very large or obesecardiac arrest patients because the chest cannot be compressed enough tocause blood flow. Additionally, chest compression via pneumatic devicesis hampered in its application to females due to the lack of provisionfor protecting the breasts from injury and applying compressive force todeformation of the thoracic cavity rather than the breasts.

CPR and chest compression should be initiated as quickly as possibleafter cardiac arrest to maximize its effectiveness and avoid neurologicdamage due to lack of blood flow to the brain. Hypoxia sets in about twominutes after cardiac arrest, and brain damage is likely after aboutfour minutes without blood flow to the brain. Further, the severity ofneurologic defect increases rapidly with time. A delay of two or threeminutes significantly decreases the chance of survival and increases theprobability and severity of brain damage. However, CPR and ACLS areunlikely to be provided within this time frame. Response to cardiacarrest is generally considered to occur in four phases, including actionby Bystander CPR, Basic Life Support, Advanced Cardiac Life Support, andthe Emergency Room. Bystander CPR occurs, if at all, within the firstfew minutes after cardiac arrest. Basic Life Support is provided byFirst Responders who arrive on scene about 4 to 6 minutes after beingdispatched to the scene. First responders include ambulance personnel,emergency medical technicians, firemen and police. They are generallycapable of providing CPR but cannot provide drugs or intravascularaccess, defibrillation or intubation. Advanced Life Support is providedby paramedics or nurse practitioners who generally follow the firstresponders and arrive about 8 to 15 minutes after dispatch. ALS isprovided by paramedics, nurse practitioners or emergency medical doctorswho are generally capable of providing CPR, and drug therapy, includingintravenous drug delivery, defibrillation and intubation. The ALSproviders may work with a patient for twenty to thirty minutes on scenebefore transporting the patient to a nearby hospital. Thoughdefibrillation and drug therapy are often successful in reviving andsustaining the patient, CPR is often ineffective even when performed bywell trained first responders and ACLS personnel because chestcompression becomes ineffective as the providers become fatigued. Thus,the initiation of CPR before arrival of first responders is critical tosuccessful life support. Moreover, the assistance of a mechanical chestcompression device during the Basic Life Support and Advanced LifeSupport stages is needed to maintain the effectiveness of CPR.

SUMMARY

The devices described below provide for circumferential chestcompression using a device which is compact, portable or transportable,self-powered with a small power source, and easy to use by bystanderswith little or no training. Additional features may also be provided inthe device to take advantage of the power source and the structuralsupport board contemplated for a commercial embodiment of the device.

The device includes a broad belt which wraps around the chest and isbuckled in the front of the cardiac arrest patient. The belt isrepeatedly tightened around the chest to cause the chest compressionnecessary for CPR. The buckles and/or front portion of the belt areanatomically accommodating for the female breast, or for the obeseperson, so that the device is effective for women as well as men. Thebuckle may include an interlock which must be activated by properattachment before the device will activate, thus preventing futile beltcycles. The operating mechanism for repeatedly tightening the belt isprovided in a support board or in a small box locatable at the patient'sside, and comprises a rolling mechanism which takes up the intermediatelength of the belt to cause constriction around the chest. The roller ispowered by a small electric motor, and the motor is powered by batteriesand/or standard electrical power supplies such as 120V householdelectrical sockets or 12V DC automobile power sockets (car cigarettelighter sockets). The belt is contained in a cartridge which is easilyattached and detached from the motor box. The cartridge itself may befolded for compactness. The motor is connected to the belt through atransmission that includes a cam brake and a clutch, and is providedwith a controller which operates the motor, clutch and cam brake inseveral modes. One such mode provides for limiting belt travel accordingto a high compression threshold, and limiting belt travel to a lowcompression threshold. Another such mode includes holding the belt tautagainst relaxation after tightening the belt, and thereafter releasingthe belt. Respiration pauses, during which no compression takes place topermit CPR respiration, can be included in the several modes. In otherembodiments, the motor is connected to the belt through a transmissionthat includes a non-reversing coupling, permitting simplified operationof the system, and brakes are connected to the system through take-offsfrom the drive train. Thus, numerous inventions are incorporated intothe portable resuscitation device described below.

The portable resuscitation device may incorporate a number of featuresand accessories that aid in the administration of CPR and other therapy.Bystanders may be unable to confidently determine if chest compressionis needed, or when it should be stopped. Accordingly, the device may becombined with an interlock system including a heart monitor or EKG whichdiagnoses the condition of the patient, and circuitry or a computerwhich initiates, permits or forbids belt operation accordingly. Thepower supply provided for belt constriction may also be used to providepower for defibrillation (an appropriate treatment for many cardiacarrests). Again, bystanders will most likely not be capable ofdetermining when defibrillation is appropriate, and the defibrillationportion of the device may be provided with an interlock system includingthe heart monitor or EKG which diagnoses the condition of the patientand circuitry which initiates, permits, or forbids defibrillation.Expert systems implemented through the circuitry or computer modules canaccomplish these functions.

Automatic, computer driven therapy of this nature may provide early andappropriate life saving response to many cardiac arrest patients whowould otherwise die. However, some situations in which the device mightbe used call for expert supervision of the CPR process by emergencymedical technicians, emergency room doctors, or cardiologists. To thisend, the expert systems mentioned above may be replaced with the expertdiagnosis and decision-making of medical personnel through a telemetrysystem housed within the support board of the device. The support boardcan include a telemetry system which automatically dials medicalpersonnel in a nearby hospital, emergency medical crew, ambulance, oreven a central diagnostic and control facility. Interlocks, limitswitches and other typical sensors can be used to sense the properposition and closure of the belt about the chest of the patient. Heartmonitors and EKG electrodes can sense the heart rate and EKG of thevictim. Using communication equipment within the device, thisinformation can be communicated from the device to medical personnelremote from the victim. Through the same system, the medical personnelcan communicate with the device to initiate, permit or prohibit beltconstriction or defibrillation, as dictated by preferred medicalprocedures. Communication can be established through normal telephonelines and a cordless telephone, or through a cellular telephone system,paging system, internet or any other communications system. The devicecan be programmed with location information, or provided with GPScapabilities to determine the location of the device, and thisinformation can be automatically transmitted to an emergency responsesystem such as the 911 system when the system is placed in use.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overview of the resuscitation device, showing the inner andouter vests partially open.

FIG. 2 is an overview of the resuscitation device in the buckledconfiguration.

FIG. 3 is an detail view of the buckle used to close the device about avictim.

FIG. 4 shows the spool assembly used to operate the compression belt.

FIG. 5 shows an alternative embodiment of the spool assembly used tooperate the compression belt.

FIG. 6 is a view of the resuscitation device properly positioned on avictim.

FIG. 7 shows the resuscitation device fitted with a number of additionaldevices for use during resuscitation.

FIG. 8 shows a detail view of the CPR module of FIG. 7.

FIG. 9 shows a detail view of the defibrillation module of FIG. 7.

FIG. 10 shows a detail view of the airway management module of FIG. 7.

FIG. 11 shows a detail view of the control and communications module ofFIG. 7.

FIG. 12 shows a block diagram of the communications system.

FIG. 13 is a block diagram of the motor control system.

FIG. 14 is an overview of the resuscitation device.

FIG. 15 illustrates the installation of the belt cartridge.

FIG. 16 illustrates the operation of the belt cartridge.

FIG. 17 illustrates the operation of the belt cartridge.

FIG. 18 illustrates an alternative configuration of the belt cartridge.

FIG. 19 illustrates an alternative configuration of the belt cartridge.

FIG. 20 illustrates an alternative configuration of the belt cartridge.

FIG. 21 illustrates an alternative configuration of the belt cartridge.

FIG. 22 illustrates an alternative configuration of the belt cartridge.

FIG. 23 illustrates an alternative embodiment of the belt.

FIG. 24 illustrates an alternative embodiment of the belt.

FIG. 25 illustrates the configuration of the motor and clutch within themotor box.

FIG. 26 illustrates the configuration of the motor and clutch within themotor box.

FIG. 27 shows a shield which is interposed between the motor box and thepatient.

FIG. 28 is a table of the motor and clutch timing in a basic embodiment.

FIG. 28a is a diagram of the pressure changes developed by the systemoperated according to the timing diagram of FIG. 28.

FIG. 29 is a table of the motor and clutch timing in a basic embodiment.

FIG. 29a is a diagram of the pressure changes developed by the systemoperated according to the timing diagram of FIG. 29.

FIG. 30 is a table of the motor and clutch timing for squeeze and holdoperation of the compression belt.

FIG. 30a is a diagram of the pressure changes developed by the systemoperated according to the timing diagram of FIG. 30.

FIG. 31 is a table of the motor and clutch timing for squeeze and holdoperation of the compression belt.

FIG. 31a is a diagram of the pressure changes developed by the systemoperated according to the timing diagram of FIG. 31.

FIG. 32 is a table of the motor and clutch timing for squeeze and holdoperation of the compression belt.

FIG. 32a is a diagram of the pressure changes developed by the systemoperated according to the timing diagram of FIG. 32.

FIG. 33 is a table of the motor and clutch timing for squeeze and holdoperation of the compression belt.

FIG. 33a is a diagram of the pressure changes developed by the systemoperated according to the timing diagram of FIG. 33.

FIG. 34 is a table of the motor and clutch timing for squeeze and holdoperation of the compression belt.

FIG. 34a is a diagram of the pressure changes developed by the systemoperated according to the timing diagram of FIG. 34.

FIG. 35 is a table of the motor and clutch timing for squeeze and holdoperation of the compression belt.

FIG. 35a is a diagram of the pressure changes developed by the systemoperated according to the timing diagram of FIG. 35.

FIG. 36 is table of the motor and clutch timing for operation of thecompression belt in an embodiment in which the system timing is reseteach time an upper threshold is achieved.

FIG. 36a is a diagram of the pressure changes developed by the systemoperated according to the timing diagram of FIG. 36.

FIG. 37 illustrates an embodiment of the chest compression device with asternal bladder.

FIG. 38 illustrates an alternative embodiment of the chest compressionbelt with single layer pull straps connecting the belt to the drivespool.

FIG. 39 illustrates an embodiment of the chest compression belt withnon-torquing spooling segment connecting the belt to the drive spool.

FIG. 40 illustrates an embodiment of the chest compression belt withsingle layer pull straps connecting the belt to the drive spool.

FIG. 41 illustrates a mechanism for connecting the chest compressionbelt to the drive spool.

FIG. 42 illustrates an embodiment of the chest compression device with aspinal support plate.

FIG. 43 is a cross section of the chest compression device with asternal bladder.

FIG. 44 is a cross section of the chest compression device with asternal bladder, shown during compression.

FIG. 45 is a cross section of the chest compression device without asternal bladder, shown during compression, illustrating a roundingeffect that may occur in some patients.

FIG. 46 is a cross section of the chest compression device with theguide spindles laterally spaced from each other to alter the forceprofile of the compression belt.

FIG. 47 is a view of the motor box with a no-back reversing drivemechanism.

FIG. 48 is a table of the motor box with a no-back reversing drivemechanism.

FIG. 49 illustrates the relationship between the change in thoracicvolume versus the change in thoracic pressure.

FIG. 50 illustrates the relationship between the slope of the curve inFIG. 49 and the actual pressure in the bladder.

FIGS. 51 and 52 illustrate additional embodiments of the motor and drivetrain used to drive the drive spool.

FIG. 53 is a graph of the actual and setpoint pressures for a series ofcompressions performed by the system for calibration purposes.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a simplified version of the resuscitation device 1. Themechanisms used for compressing the chest includes compression assembly2 which includes a chest compression belt 3 with buckles 4L and 4R, afriction liner 5, a support board 6 and a motor driven spool assembly 7.The support board 6 is placed under a cardiac arrest victim, and thecompression belt 3 and friction liner 5 are wrapped around the victim'schest. The chest compression belt, having a left side 3L and a rightside 3R, is buckled over the victims chest by latching the buckles 4Land 4R together. In this configuration, the friction liner 5 will fitbetween the chest compression belt 3 and the victim and any clothes wornby the victim. The compression belt may be made of any strong material,and sail cloth has proven adequate for use. The compression belt mayalso be referred to as a vest, corset, girdle, strap or band. Thefriction liner may be made of Teflon®, Tyvek® or any other low frictionmaterial (by low friction, we mean a material that will permit slidingof the compression belt with less friction than expected between thebelt and the victims clothing or bare skin). The friction liner may bemade with any suitable lining material, as its purpose is to protect thevictim from rubbing injury caused by the compression belt, and it mayalso serve to limit frictional forces impeding the compression beltoperation. The friction liner can be provided in the form of a belt,vest, corset, girdle, strap or band, and may partially or completelyencircle the chest.

The front of the compression belt 3, including the buckles 4L and 4R,are configured to provide a broad pressure point over the sternum of thevictim. This is illustrated in FIG. 2. Large openings 8 may be providedto accommodate female breasts and obese male breasts. The underside ofthe buckles 4L and 4R are smooth and broad, to distribute compressiveforce evenly over a wide area of the chest corresponding to the sternum.The point at which the buckle attaches to the chest compression belt mayvary considerably, from the front of the chest to the back of thecompression assembly, and the openings 8 may be provided in the bucklesrather than the belt itself. FIG. 3 shows a detail of the buckles 4 usedto fasten the compression belt about the chest of the victim. The bucklemay be of any type, and preferably includes a latch sensing switch 9operably connected through wire 10 to the motor control system (see FIG.13) to indicate that the device has been buckled about the victims chestand is ready for the initiation of compression cycles. The buckles shownin FIG. 3 are D-ring shaped buckles with large openings 8, attached tothe compression belt 3. Other fasteners and fastening means may be used.

The chest compression belt 3 is repeatedly tightened about the chest ofa victim through the action of one or more tightening spools which makeup the spool assembly 7 located within the support board 6. The spoolassembly, illustrated in FIG. 4, includes at least one spool or reelconnected to the compression belt 3 at the back of the belt, preferablynear the center or saggital line 11 (See FIGS. 1 and 2) of thecompression belt (although it may be located on the front or side ofcompression belt). FIG. 4 shows a view of the spool assembly 7 and itsattachment to the compression belt 3. A spool assembly includes a singledrive spool 12 operably connected to the motor 14 through drive shaft15. The compression belt is secured to the drive spool in any suitablemanner. In this case a longitudinal slot 16 is provided in the drivespool 12. The slot extends radially or chordally through the drive spooland extends axially for a length corresponding to the width of thecompression belt, leaving the ends 17 of the drive spool solid forconnection to the drive shaft 15 and journal shaft 18. The belt isslipped through the slot to created a secure connection between the beltand the drive spool. When secured in this manner, the rotation of thedrive spool 12 will take up the right side of the compression belt 3Rand the left side of the compression belt 3L and roll them up onto thespool, thus tightening the compression belt about the chest of thevictim wearing the device. Spindles or alignment rollers 19 provide foralignment and low friction feed of the belt onto the roll created byoperation of the drive shaft.

Many alternative embodiments can be envisioned for the rollingmechanism, and one such alternative is illustrated in FIG. 5. Spools 12Land 12R are aligned in parallel and interconnected by a transmissiongear 20 and planetary gear 21 and journaled upon shafts 18L and 18R. Thedrive shaft 15 is attached to spool 12R (or spool 12L) and operablyattached to motor 14. The motor turns the shaft 15 and spool 12R in acounterclockwise direction to pull the right side of the compressionbelt 3R to the left and roll onto the spool. The transmission gear 20acts upon the planetary gear 21 to cause clockwise rotation of spool12L, which in turn pulls and wraps the left side of the compression belt3L onto the spool 12L.

Thus, many embodiments of mechanisms which can cause repeated cyclictightening of the compression vest about the chest of the victim may beenvisioned. The compression belt serves to radially compress the chestthrough the cooperative action of the belt, board, and buckle, and todisperse the compressive force around the chest.

The motor is energized to rotate the spools and cause the compressionbelt to constrict around the chest of a victim. A motor such as abattery operated hand drill motor provides adequate chest compressionfor the purposes of CPR. To cause repetitive constriction of thecompression belt 3, the motor 14 must be attached via a clutch 22 orother such mechanism. The motor 14 may be attached to the drive shaft 15through a torque slipping clutching mechanism which engages the driveshaft until a high torque is achieved (indicating great resistance tofurther constriction, and thus indicating that the victim's chest hasbeen compressed), and releases automatically upon such high torque, onlyto re-engage after the belt has been expanded in response to the normalelastic expansion of the victim's chest. In this manner, repetitivecompression is achieved without need to repeatedly energize andde-energize the motor, thereby extending the length of operating timefor any given battery supply. Alternatively, the motor may be repeatedlyenergized and de-energized, with the spools spinning freely duringperiods in which the belt is de-energized, wherein the clutch mechanism22 will be similar to clutch mechanisms used on electric drills (whichengage during operation of the drill but spin freely when the drill isde-energized). While the natural elastic expansion of the chest shouldmake it unnecessary to drive the belt toward a loose condition, positiveloosening may be achieved by reversing the motor or reversing the actionof the motor through appropriate clutch or gear mechanisms. Timing ofcompressions is regulated through a computer module or a simple relay(windshield wiper style relays), and preferably will conform to standardof the Advanced Cardiac Life Support guidelines or CardiopulmonaryResuscitation guidelines, or any other medically acceptableresuscitation regime. Current guidelines put forth by the American HeartAssociation call for 60 to 100 chest compressions per minute.

The motor is preferably battery powered, with provisions for takingpower from any available power source. Batteries 23 may be stored withinthe support board 6. Three volt batteries of convenient size, alreadyavailable for use with numerous power tools, provide about five minutesof compression per battery, while twelve-volt batteries (1700 mA-h perbattery) have provided about ten minutes of compression per battery. Athirty minute total battery capacity is desirable (corresponding to theestimated average time between cardiac arrest and transport to thehospital). Accordingly, several batteries may be installed within thesupport board and electrically connected to the motor and itscontroller. The batteries are provided with a trickle charge through acharger socket and charger plugged into 120V AC power when the device isnot in use. (It is intended that the device be installed in factories,office buildings, airplanes and other facilities with relatively stablesources of power, and that the unit remain plugged in and charging whennot in use.) If AC power is readily available at the site of use, thedevice may continue to run on AC power to preserve the batteries forlater use. The unit may also be plugged into an automobile power jackwith an appropriate auto adapter, thus providing for use where anautomobile is the only source of power, and for extended use in anambulance.

FIG. 6 shows the resuscitation device installed on a cardiac arrestvictim. The support board 6 is placed under the victim, and the right 3Rand left 3L portions of the compression belt are wrapped around thevictim's chest and buckled over the front of the chest, indicated byarrow 25. Once in place, the system may be put into operation bymanually starting the motors or by automatic initiation given the properfeedback from sensors located on the device, including the buckle latchsensors

A number of features may be combined with the basic system describedabove. The structure necessary for housing the operating mechanism forthe belt, referred to as the support board above, can serve also asstorage for additional devices used during resuscitation. FIG. 7illustrates the resuscitation device 1 in a potential commercialembodiment. The support board is sized to reach approximately from thelower lumbar region to the shoulders of a victim. The compression module26 is separable from the support board, and includes the compressionbelt and friction vest stored within the compression module. The spoolassembly and motor are also stored within the compression module,although the motor may also be installed in the support board. In thisfigure, the compression module comprises a small support board 27 whichfits into the larger system support board 28. Taking advantage ofavailable space in the system support board, a compartment 29 forstorage of airway management devices (bag masks, oxygen masks, etc.),and a compartment 30 for storage of defibrillation equipment (electrodesand paddles, etc.) are included with the support board.

A control and communication module 31 may also be incorporated into thesupport board. A small oxygen bottle 32 may be included, along withhoses routed to an accessible point on the board, and any connectordesired for connection between the oxygen bottle and devices provided inthe airway management compartment. Batteries 23 are stored within thesupport board (the number of the batteries chosen according the desiredoperating time, and the placement of the batteries dictated by availablespace). Batteries are operably connected to the motor in the compressionmodule through electrical connectors 33 and appropriate wiringthroughout the support board. The batteries can also be operablyconnected to the defibrillation module and control and communicationsmodule. Although long life batteries can be used, rechargeable batteriesmay be preferred. Accordingly, charging connection 34 on the supportboard is provided for charging the batteries or operating the devicethrough outside power supplies.

The device is intended to be stored for long periods of time betweenuses, and storage holder 35 is provided for this purpose. The storageholder can include such necessities as power supply connectors, a powerplug, and a charging transformer. A removal sensor 36 is included in thesupport board to sense when the support board is removed from thestorage holder (which, as described below, can be used as a conditionindicating use of the device, and therefore the need to alert emergencymedical personnel). The removal sensor can comprise a simple limitswitch which senses physical removal of the system, and the limit switchcan be used as a power switch or awaken switch which starts initiationof the system. The removal sensor can comprise a current sensor on thecharging lines which treat cessation of charging current, increase incurrent draw through the charging system, or motor current as anindication of use. The choice of sensor may be made with many practicalconsiderations in mind, such as the desire to avoid treating poweroutages as indications of use and other such unintended initiations. Thestate in which the device is deemed to be “in use” can be chosenaccording to the practical considerations, and in most instances it isexpected that mere removal of the resuscitation device from the holderwill constitute a clear signal someone has determined that a victimrequires its use, and that emergency medical personnel should bedispatched to the location of the device. There are some environments inwhich later conditions will be used to indicate that the device is “inuse,” such as when installed in ambulances, airplanes, hospitals orother environments where it might be advisable to remove the device fromits storage holder as a precaution or preparatory measure, and delayinitiation of communications until the device is deployed or installedon the victim. In such cases, the buckle latch shown in FIG. 3 can beused as the sensor that indicates that the resuscitation device is inuse.

FIG. 8 shows the details of the compression module 26. When not in use,the module is covered with a tear sheet 37 which protects thecompression belt from wear. The buckles 4 are readily visible under thetear sheet. The electrical connectors 38 connect the batteries in thesupport board with the motor inside the compression module. The insideof the compression belt 3 is fitted with penetrating electrodes 39 inthe right sternum parasaggital location 40 (See FIG. 6) and left ribmedial location 41 (See FIG. 6) for establishing the electrode contactneeded for EKG sensing. These electrodes may be dispensed with inenvironments where proper placement of the defibrillation electrodes canbe assumed due to a high level of training amongst likely bystanders andfirst responders. The friction vest 5 is secured to the compressionmodule above the spool assembly location.

FIG. 9 shows a detail view of the defibrillation module 30. Thedefibrillation module includes a pair of defibrillation electrodes 42connected to the batteries through the power connections 43. Thedefibrillation electrodes will be controlled by circuitry housed withinthe defibrillation module, and may be connected to the control modulethrough the data port 44. The defibrillation module is releasablyattached to the support board 28 with quick release latches 51. Tearsheet 46 protects the components of the defibrillation module duringstorage and provides ready access for use.

FIG. 10 shows the detail view of the airway management module 29, whichincludes an oxygen mask 47, a length of tubing 48 and an air fitting 49connecting the oxygen mask to the oxygen bottle within the support board28. The oxygen mask serves as a blood gas exchange means, supplyingoxygen to the lungs for exchange with blood gas such as CO₂. Optionalmedicine injectors 50 may be operably connected to the masks or hose toprovide for automatic injection of ACLS medications into the airway. Theairway management module is releasably attached to the support board 28with quick release latches 51. Tear sheet 46 protects the components ofthe airway management module during storage and provides ready accessfor use. An end-tidal CO₂ monitor 52 can be included in the mask toprovide for biological feedback and monitoring of the success of theCPR. A skin mounted blood oxygen level monitor 53 can also be mounted onthe mask for the same purpose (fingertip blood oxygen sensors may alsobe used, and supplied in the overall assembly to be readily available).The biological data obtained by the sensors is transmitted to thecontrol module via appropriate wiring in the mask and support board.

FIG. 11 shows a detail view of the control and communications module.The control unit 54 is connected to the compression module,defibrillation module and the airway management module throughappropriate wiring through the support board 28. The control unit isoptionally connected to the communications unit 55. The communicationsunit includes means for communicating the EKG and other measured medicalparameters sensed on the board to the screen 56 and via telephone toremote medical personnel. The communications unit can include atelephone handset or speaker phone. Because the device is most likely tobe used at a location separate from the storage holder, thecommunications module preferably includes a wireless communicationdevice, such as wireless telephone, radio telephone or cellular, and anynecessary telephone base will be installed in the storage holder.

The communications unit and control unit are set up to operate in thefollowing manner, also illustrated in the block diagram of FIG. 12. Thedevice may remain mounted in a charging unit for months between use, andwill be removed from the charging unit for use. Upon removal of thedevice from its storage location, a sensor in the control unit sensesthe removal (through limit switches, magnetic switches, or motionsensors, current sensors in the charging system, or otherwise) andinitiates the system, checking functions, energizing a display unit andaccomplishing other typical warm-up functions. As a first step, thesystem initiates a telephone communication with a medical facilitythrough the communications unit. The communication may use anycommunication medium, whether it be standard telephone lines, cellulartelephone system, paging system or radio transmitter. The system may beset up to initiate communications with central medical facility, such asa local 911 emergency system, a nearby hospital or ambulance service, ora central facility staffed with medical personnel trained specificallyon the remote use of the device (all generally referred to as medicalpersonnel). Upon establishing communication, the communications unitinforms medical personnel of the location or identification of thedevice (which may be stored in computer memory in the communicationsunit, or determined through GPS or other such system), and thisinformation can be used to dispatch an emergency medical team to thelocation of the device. In a simple embodiment which does not require acomputer to control the actions of the alert feature, the removal sensormay comprise a limit switch, while the communications module maycomprise a simple telephone unit installed in the storage holdertogether with a tape recorded message, where the operation of the relayin response to removal of the resuscitation device includes initiationof the telephone call to 911 and playback of an alert message providingalert information such as the location of the board. The communicationsunit may also be provided with an alert button which may be operated bya bystander regardless of the use of the board to summon an emergencyteam to the location regardless of the condition of the resuscitationdevice.

Before the emergency medical team arrives, a bystander will place theboard under the victim, buckle the compression belt around the victim,and apply the defibrillation and/or sensing electrodes (or vice versa).Alternatively, sensing electrodes can be included on the inner surfaceof the compression belt. The system monitors the installation of thebelt through signals provided by the latching sensors in the buckle. Thesystem monitors biological input, which can comprise monitoring of EKGsignals from the EKG electrode patches of the defibrillation module,monitoring EKG signals measured by the belt mounted electrodes,monitoring signals from an end-tidal CO₂ monitor from the airwaymanagement module, and any other biological signal sensor incorporatedinto the device. The system can also monitor or respond to manuallyinputted instructions from the control unit, in order to provide on-siteemergency medical personnel with control of the device when they arriveon scene. During operation, the system transmits all availablebiological information, including EKG signals, blood pressure, end-tidalCO₂ and any other monitored biological parameter to the remote medicalfacility, and it can also transmit information regarding theconfiguration of the device, including battery life, system operatinglimit settings (i.e., whether the system is set for automatic operation,permissive operation, or disabled in any function) so that medicalpersonnel can ensure that the appropriate configuration is in effect.

Communication with the medical facility will allow emergency medicalpersonnel to diagnose the condition of the patient and, through signalssent from the medical personnel to the communications unit, permit,initiate or prohibit certain additional therapeutic ACLS actions. Forexample, upon diagnosing the EKG conditions which indicate the need fordefibrillation, the medical personnel can send a signal to thecommunications unit which acts upon the control unit to permit manualoperation of the defibrillation electrodes by the bystander. The systemalso provides for application of a defibrillation shock via remotesignal from the medical personnel. The device can incorporate an expertsystem such as the Automatic External Defibrillator. The medicalpersonnel can also communicate other actions and ensure that certainacts are undertaken by the bystander through the communication system.For example, the medical personnel may communicate verbally with thebystander to ascertain the cause of the cardiac arrest, the properplacement of the oxygen mask, appropriate clearing of the airway, andother information. Where the airway management module is provided withmedication such as epinephrine, lidocaine, bretylium or other drugscalled for in the ACLS guidelines (or newly proposed drugs such as T3),the medical personnel can instruct bystanders to inject the appropriatemedication through the airway. Where automatic injectors such as thosedescribed in Kramer, Interactive External Defibrillation and DrugInjection System, U.S. Pat. No. 5,405,362 (Apr. 11, 1995) are provided,or similar system with non-osseous injectors are provided, the medicalpersonnel can instruct bystanders to inject appropriate medicationthrough these injectors. Where the injectors are provided with means forautomatic operation based on measured EKG signals, blood pressure andend-tidal CO₂, the medical personnel can send signals to the system toinitiate injection by remote control of the medical personnel, permitinjection by local control as determined by the expert system, permitinjection by bystanders, or prohibit injection by the system orbystanders. For example, the system can be initially set up to forbidany injection. Medical personnel, having diagnosed ventricularfibrillation through the information provided by the communicationsunit, can send an appropriate signal to permit or initiate injection ofepinephrine, and also send a signal to prohibit injection of atropineuntil called for under the ACLS guidelines. A newly proposed drug T3 canbe administered through the airway, into the lungs, as a therapy forcardiac arrest. Controlled injection into the airway can be initiated orprohibited in the same manner. Thus, all actions in the ACLS, includingcompression, defibrillation, drug injection can be accomplished throughthe system under the guidance of medical personnel from a remotelocation, or they may be accomplished through expert systems installedin the control module. Each of these functions is incorporated into asystem that automatically initiates communication with medical personneland informs medical personnel of the location of the device so thatemergency medical personnel may be dispatched to the location.

The repeated compression will be initiated upon buckling of thecompression belt (automatically) or a switch can be provided for thebystander to initiate compression. The system will continue compressioncycles, until de-activated, according the motor control block diagram ofFIG. 13. Upon initiation of the system, the control unit will monitorinstallation of the belt via appropriate sensors in the buckles orthrough other sensors. When the motor control 57 receives the initiatecompression signal from the control unit, the motor is started. Themotor is preferably run continuously, rather than stopped and started,to avoid repeated application of startup current and thus conservebattery power. When the motor is up to speed, the clutch is engaged. Asa baseline, the clutch is engaged every second for one-half second. Thiscyclic engagement of the clutch continues repeatedly for five cycles, asrecommended by current CPR guidelines, and then is interrupted for arespiration pause, if desired. To avoid excessive drain on thebatteries, the motor controller includes a torque sensor (sensingcurrent supply to the motor, for example), and monitors the torque orload on the motor. A threshold is established above which furthercompression is not desired or useful, and if this occurs during the halfsecond of clutch engagement, then the clutch is disengaged and the cyclecontinues. The system can monitor the effectiveness of the compressionstroke by monitoring the Co₂ content of the victim's exhalant. Where CO₂content is low, indicating inadequate circulation, the control systemincreases the torque limit until the CO₂ levels are acceptable (or untilthe maximum torque of the motor is achieved.) This is another example ofthe device's use of biological signals to control operation of thesystem. The cycle time and period, number of cycles between respirationpauses, and the torque limit, can be set according to currentguidelines, and can also be varied by the remote medical personnel viathe remote control capabilities of the control unit.

FIG. 14 shows an overview of the resuscitation device 61. The majorcomponents are provided in modular form, and include the motor box 62,the belt cartridge 63 and the belt 64. The motor box exterior includes asprocket 65 in a drive wheel 66 which releasable mates with thereceiving rod 67 on the cartridge. The cartridge houses the belt whichwill wrap around the chest of the patient. The cartridge also includesthe spool 68 which is turned by the receiving rod. The spool takes upthe midpoint of the belt to drive the compression cycles. A computercontrol system 70 may be included as shown in an enclosure mounted onthe motor box. By providing the system in modular form, with the motorbox releasable attached to the belt cartridge, the belt cartridge maymore easily be maneuvered while slipping it under the patient.

FIG. 15 shows a more detailed view of the cartridge, including theinternal mechanisms of the belt cartridge 63. The outer body of thecartridge provides for protection of the belt during storage, andincludes a back plate 71 with a left panel 71L and a right panel 71R(relative to the patient during use). The right plate can be folded overthe left plate for storage and transport. Both panels are covered with asheet 72 of low friction material such as PTFE (Teflon®) to reducefriction when the belt slides over the panel during operation. Under theleft panel, the cartridge has a housing 73 which houses the middleportion of the belt, the spool 68 and the spindle 75 (See FIG. 16). Thelateral side 74 of the cartridge (corresponding to the anatomic positionwhen in use on a patient) houses the drive spool 68, with its drive rod67 which engages the drive wheel 66 (See FIG. 14) of the motor box. Thecartridge also houses the guide spindle 75 (visible in FIG. 16) fordirecting the belt toward the drive spool 68. The guide spindle islocated near the center of the cartridge (corresponding to the medialline of the patient when in use), so that it is located near the spinewhen the device is in use. This spindle reverses the belt travel for theleft side of the belt, so that when it is pulled to the left by thedrive spool, the portion that wraps around the left flank of the bodymoves to the right. The cartridge body is also hinged near the mid-line,and in this view the cartridge is hinged near the axis of the spindle. Afriction liner 76 is suspended over the belt in the area of the guidespindle, and is attached to the housing at the top and bottom panels 73t and 73 b and spans the area in which the left belt portions and rightbelt portions diverge from the cartridge. The belt 64 is shown in theopen condition. Male quick release fittings 77R on the right beltportion fit into corresponding female quick release 77L fittings on theleft belt portion to releasably secure the belt around the patient'schest. The belt length on the left and right sides of the belt may beadjusted so that the buckles fall just over the center of the patient'schest during operation, or they may be adjusted for placement of thebuckles elsewhere around the chest. The handle 78 is provided forconvenient handling and carrying of the device.

FIG. 16 shows a cross section of the belt cartridge. The housing 73 isrelatively flat, (but may be wedge shaped to assist in sliding it undera patient) when viewed from the superior position. The left panel 71Lsits atop the housing 73 and the right panel extends from the housing.In the unfolded position, the cartridge is flat enough to be slippedunder a patient from the side. In the cross-sectional view, the guidespindle 75 can be seen, and the manner in which the belt is threadedthrough the slot 69 of the drive spool 68 appears more clearly. The belt64 comprises a single long band of tough fabric threaded through thedrive spool slot 69 and extending from the drive spool to the right sidequick releases 77R and also from the drive spool, over and around theguide spindle, and back toward the drive spool to the left side quickreleases 77L. The belt is threaded through the drive spool 68 at itsmid-portion, and around the guide spindle, where the left belt portion64L folds around the guide spindle, under the friction liner and back tothe left side of the cartridge, and the right belt portion 64R passesthe spindle to reach around the patient's right side. The friction beltliner 76 is suspended above the guide spindle and belt, being mounted onthe housing, and fits between the patient and the compression belt. Thecartridge is placed under the patient 80, so that the guide spindle islocated close to the spine 81 and substantially parallel to the spine,and the quick release fittings may be fastened over the chest in thegeneral area of the sternum 82.

In use, the cartridge is slipped under the patient 80 and the left andright quick releases 77L and 77R are connected. As shown in FIG. 17,when the drive spool is rotated, it takes up the middle portion of thebelt and tightens the belt around the chest. The compression forceexerted by the belt is more than sufficient to induce or increaseintrathoracic pressure necessary for CPR. When the belt is spooledaround the drive spool 68, the chest of the patient is compressedsignificantly, as illustrated.

While it will usually be preferred to slide the cartridge under thepatient, this is not necessary. The device may be fitted onto thepatient with the buckles at the back or side, or with the motor to theside or above the patient, whenever space restrictions require it. Asshow in FIG. 18, the cartridge may be fitted onto a patient 80 with onlythe right belt portion 64R and right panel 71R slipped under thepatient, and with the right panel and left panel partially unfolded. Theplacement of the hinge between the right side and left side panelspermits flexibility in installation of the device.

FIGS. 19 through 22 show that the cartridge may also be fitted onto apatient 80 with both the right panel 71R and the left panel 71L slippedunder the patient, but with the motor box 62 folded upward, rotatedabout the axis of the drive spool 68. These configurations are permittedby the modular nature of the motor box connection to the belt cartridge,and will prove useful in close spaces such as ambulances andhelicopters. (Note that, although the belt may be tightened by spoolingoperation in either direction, tightening in the direction of arrow 83,clockwise when viewed from the top of the patient and the device, willcause reactive force which urges the motor box to rotate into thedevice, toward the body, rather than outwardly away from the body.Locking pins may be provided to prevent any rotational movement betweenthe motor box and the cartridge. In the construction of the motor box asshown, the limited height of the box (the height of the box is less thanthe distance between the left flank of the patient and the drive spool)prevents contact with the patient in case the locking pins are notengaged for any reason. The rotation of the drive belt may be reversedto a counter clockwise direction, in which reactive force will urge themotor box to rotate outwardly. In this case, locking mechanisms such aslocking pins can be used to protect operators from movement of thesystem.)

Regardless of the orientation of the panels, the reversing spindle willproperly orient the travel of the belt to ensure compression. Theplacement of the spindle at the point where the right belt portion andthe left belt portion diverge under the patient's chest, and theplacement of this spindle in close proximity to the body, permits thebelt to make contact with the chest at substantially all points on thecircumference of the chest. The position of the spindle reverses thetravel of the belt left portion 64L from a transverse right to leftdirection to a transverse left to right direction, while the fact thatbelt right portion 64R bypasses the spindle means that it always movesfrom right to left in relation to the patient when pulled by the drivespool. Thus the portions of the belt engaging the chest always pull fromopposite lateral areas of the chest to a common point near a centralpoint. In FIGS. 16 and 17, the opposite lateral areas correspond to theanatomic lateral area of the patient, and the central point correspondsto the spine. In FIG. 18, the lateral areas correspond to the spine andanterior left side of the torso, while the central point corresponds tothe left lateral area of the chest. Additionally, the use of the singlespindle at the center of the body, with the drive spool placed at theside of the body, permits simple construction and the detachable ormodular embodiment of the motor assembly, and allows placement of thebelt about the patient before attachment of the motor box to the entiredevice.

FIG. 20 illustrates an embodiment of the compression belt which reducesthe take up speed for a given motor speed or gearing and allows fortwice the compressive force for a given motor speed. The compressionbelt comprises a loop 84 of belt material. The loop is threaded throughthe complex path around spindles 85 in the quick release fasteners 86,around the body to the guide spindle 75, around or past the guidespindle and into the drive spool 68. The left belt portion outer layer87L and right belt portion outer layer 87R form, together with the leftbelt portion inner layer 88L and right belt portion inner layer 88R forma continuous loop running inwardly from the fastener spindle, inwardlyaround the chest to the opposite fastener spindle, outwardly from theopposite fastener spindle, downwardly over the chest, past the guidespindle to the drive spool, through the drive spool slot and back underthe guide spindle, reversing around the guide spindle and upwardly overthe chest back to the fastener spindle. Thus both the inner and outerlayers of this two layer belt are pulled toward the drive spool to exertcompressive force on the body. This can provide for a decrease infriction as the belts will act on each other rather than directly on thepatient. It will also allow for a lower torque, higher speed motor toexert the necessary force.

In FIG. 21, the double layer belt system is modified with structurewhich locks the inner belt portion in place, and prevents it from movingalong the body surface. This has the advantage that the major portion ofthe belt in contact with the body does not slide relative to the body.To lock the belt inner layer in place relative to the loop pathway, thelocking bar 89 is fixed within the housing 73 in parallel with the guidespindle 75 and the drive spool 68. The inner loop may be secured andfastened to the locking bar, or it may be slidably looped over thelocking bar (and the locking bar may be rotatable, as a spindle). Theleft belt portion outer layer 87L and right belt portion outer layer 87Rare threaded through the drive spool 68. With the locking bar installed,the rotation of the drive spool takes up the outer layer of the belt,and these outer layers are forced to slide over the left belt portioninner layer 88L and right belt portion inner layer 88R, but the innerlayers do not slide relative to the surface of the patient (except,possibly, during a brief few cycles in which the belt centers itselfaround the patient, which will occur spontaneously due to the forcesapplied to the belt.

In FIG. 22, the double layer belt system is modified with structurewhich does not lock the inner belt portion in place or prevent it frommoving along the body surface, but instead provides a second drive spoolto act on the inner layer of the belt. To drive the belt inner layerrelative to the loop pathway, the secondary drive spool 90 is fixedwithin the housing 73 in parallel with the guide spindle 75 and thedrive spool 68. This secondary drive spool is driven by the motor,either through transmission geared within the housing or through asecond receiving rod protruding from the housing and a secondary drivesocket driven through appropriate gearing in the motor box. The innerloop may be secured and fastened to the secondary drive spool, or it maybe threaded through a secondary drive spool slot. The left belt portionouter layer 87L and right belt portion outer layer 87R are threadedthrough the first drive spool 68. With the secondary drive spool, therotation of the first drive spool 68 takes up the outer layer of thebelt, and these outer layers are forced to slide over the left beltportion inner layer 88L and right belt portion inner layer 88R, whilethe secondary drive spool takes up the inner layers.

The compression belt may be provided in several forms. It is preferablymade of some tough material such as parachute cloth or Tyvek®. In themost basic form shown in FIG. 23, the belt 64 is a plain band ofmaterial with fastening ends 92L and 92R, corresponding left and rightbelt portions 64L and 64R, and the spool engaging center portion 93.While we have used the spool slot in combination with the belt beingthreaded through the spool slot as a convenient mechanism to engage thebelt in the drive spool, the belt may be fixed to the drive spool in anymanner. In FIG. 24, the compression belt is provided in two distinctpieces comprising left and right belt portions 64L and 64R connectedwith a cable 94 which is threaded through the drive spool. Thisconstruction permits a much shorter drive spool, and may eliminatefriction within the housing inherent in the full width compression bandof FIG. 23. The fastening ends 92L and 92R are fitted with hook and loopfastening elements 95 which may be used as an alternative to other quickrelease mechanisms. To provide a measurement of belt pay-out and take-upduring operation, the belt or cable may be modified with the addition ofa linear encoder scale, such as scale 96 on the belt near the spoolengaging center portion 93. A corresponding scanner or reader may beinstalled on the motor box, or in the cartridge in apposition to theencoder scale.

FIG. 25 illustrates the configuration of the motor and clutch within themotor box. The exterior of the motor box includes a housing 101, and acomputer module 70 with a convenient display screen 102 for display ofany parameters measured by the system. The motor 103 is a typicallysmall battery operated motor which can exert the required belttensioning torque. The motor shaft 104 is lined up directly to the brake105 which includes reducing gears and a cam brake to control freespinning of the motor when the motor is not energized (or when a reverseload is applied to the gearbox output shaft). The gearbox output rotor106 connects to a wheel 107 and chain 108 which connects to the inputwheel 109, and thereby to the transmission rotor 110 of the clutch 111.The clutch 111 controls whether the input wheel 109 engages the outputwheel 112, and whether rotary input to the input wheel is transmitted tothe output wheel. (The secondary brake 113, which we refer to as thesecondary brake, provides for control of the system in some embodiments,as explained below in reference to FIG. 32.) The output wheel 112 isconnected to the drive wheel 66 via the chain 114 and drive wheel 66 andreceiving rod 67 (the drive rod is on the cartridge). The drive wheel 66has receiving socket 65 which is sized and shaped to mate and engagewith the drive rod 67 (simple hexagonal or octagonal sprocket whichmatches the drive rod is sufficient). While we use a wrap spring brake(a MAC 45 sold by Warner Electric) for the cam brake in the system, anyform of brake may be employed. The wrap spring brake has the advantageof allowing free rotation of the shaft when de-energized, and holds onlywhen energized. The wrap spring brake may be operated independent of themotor. While we use chains to transmit power through the system, belts,gears or other mechanisms may be employed.

FIG. 26 illustrates the configuration of the motor and clutch within themotor box. The exterior of the motor box includes a housing 101 whichholds the motor 103, which is a typical small battery operated motorwhich can exert the required belt tensioning torque. The motor shaft 104is lined up directly to the brake 105 which includes reducing gears anda cam. The gearbox output rotor 106 connects the brake to the outputwheel 107 and chain 108 which in turn connects directly to the drivewheel 66 and receiving rod 67. The drive spool 68 is contained withinthe housing 101. At the end of the drive spool opposite the drive wheel,the brake 115 is directly connected to the drive spool. The belt 64 isthreaded through the drive spool slot 69. To protect the belt fromrubbing on the motor box, the shield 117 with the long aperture 118 isfastened to the housing so that the aperture lies over the drive spool,allowing the belt to pass through the aperture into the drive spoolslot, and return out of the housing. Under the housing, slidablydisposed within a channel in the bottom of the housing, a push plate 130is positioned so that it can slide back and forth relative to thehousing. The belt right portion 64R is fitted with a pocket 131 whichcatches or mates with the right tip 132 of the push plate. The right tipof the push plate is sized and dimensioned to fit within the pocket. Bymeans of this mating mechanism, the belt can be slipped onto the pushplate, and with the handle 133 on the left end of the push plate, thepush plate together with the right belt portion can be pushed under apatient. The belt includes the encoder scale 96, which can be read withan encoder scanner mounted on or within the housing. In use, the beltright portion is slipped under the patient by fastening it to the pushplate and sliding the push plate under the patient. The motor box canthen be positioned as desired around the patient (the belt will slipthrough the drive spool slot to allow adjustment). The belt rightportion can then be connected to the belt left portion so that thefastened belt surrounds the patient's chest. In both FIGS. 25 and 26,the motor is mounted in side-by-side relationship with the clutch andwith the drive spool. With the side-by-side arrangement of the motor andthe spool, the motor may be located to the side of the patient, and neednot be placed under the patient, or in interfering position with theshoulders or hips. This also allows a more compact storage arrangementof the device, vis-à-vis an in-line connection between the motor and thespool. A battery is placed within the box or attached to the box asspace allows.

During operation, the action of the drive spool and belt draw the devicetoward the chest, until the shield is in contact with the chest (withthe moving belt interposed between the shield and the chest). The shieldalso serves to protect the patient from any rough movement of the motorbox, and help keep a minimum distance between the rotating drive spooland the patient's skin, to avoid pinching the patient or the patient'sclothing in the belt as the two sides of the belt are drawn into thehousing. As illustrated in FIG. 27, the shield 117 may also include twolengthwise apertures 134 separated by a short distance. With thisembodiment of the shield, one side of the belt passes through oneaperture and into the drive spool slot, and the other side of the beltexits from the drive spool slot outwardly through the other aperture inthe shield. The shield, as shown, has an arcuate transverse crosssection (relative to the body on which it is installed). This arcuateshape permits the motor box to lay on the floor during use while asufficient width of shield extends between the box and the belt. Theshield can be made of plastic, polyethylene, PTFE, or other toughmaterial which allows the belt to slide easily. The motor box, may,however, be placed anywhere around the chest of the patient.

A computer module which acts as the system controller is placed withinthe box, or attached to the box, and is operably connected to the motor,the cam brake, clutch, encoder and other operating parts, as well asbiological and physical parameter sensors included in the overall system(blood pressure, blood oxygen, end tidal Co₂ body weight, chestcircumference, etc. are parameters that can be measured by the systemand incorporated into the control system for adjusting compression ratesand torque thresholds, or belt pay-out and slack limits). The computermodule can also be programmed to handle various ancillary tasks such asdisplay and remote communications, sensor monitoring and feedbackmonitoring, as illustrated in our prior application Ser. No. 08/922,723.

The computer is programmed (with software or firmware or otherwise) andoperated to repeatedly turn the motor and release the clutch to roll thecompression belt onto the drive spool (thereby compressing the chest ofthe patient) and release the drive spool to allow the belt to unroll(thereby allowing the belt and the chest of the patient to expand), andhold the drive spool in a locked or braked condition during periods ofeach cycle. The computer is programmed to monitor input from varioussensors, such as the torque sensor or belt encoders, and adjustoperation of the system in response to these sensed parameters by, forexample, halting a compression stroke or slipping the clutch (or brake)in response to torque limit or belt travel limits. As indicated below,the operation of the motor box components may be coordinated to providefor a squeeze and hold compression method which prolongs periods of highintrathoracic pressure. The system may be operated in a squeeze andquick release method for more rapid compression cycles and betterwaveform and flow characteristics in certain situations. The operationof the motor box components may be coordinated to provide for a limitedrelaxation and compression, to avoid wasting time and battery power tomove the belt past compression threshold limits or slack limits. Thecomputer is preferably programmed to monitor two or more sensedparameters to determine an upper threshold for belt compression. Bymonitoring motor torque as measured by a torque sensor and paid out beltlength as determined by a belt encoder, the system can limit the belttake-up with redundant limiting parameters. The redundancy provided byapplying two limiting parameters to the system avoids over-compressionin the case that a single compression parameter exceed the safethreshold while the system fails to sense and response the threshold bystopping belt take-up.

An angular optical encoder (also referred to as a rotary encoder) may beplaced on any rotating part of the system to provide feedback to a motorcontroller relating to the condition of the compression belt. (Theencoder system may be an optical scale coupled to an optical scanner, amagnetic or inductive scale coupled to a magnetic or inductive encoder,a rotating potentiometer, or any one of the several encoder systemsavailable.) The encoder 116, for example, is mounted on the secondarybrake 113 (in FIG. 25), and provides an indication of the motor shaftmotion to a system controller. An encoder may also be placed on thedrive socket 65 or drive wheel 66, the motor 103 and/or motor shaft 104.The system includes a torque sensor (sensing current supply to themotor, for example, or directly sensing torque exerted on the drivespool), and monitors the torque or load on the motor, thereby providingan indication of the force applied to the body. For either or bothparameters, a threshold is established, above which further compressionis not desired or useful, and if this occurs during the compression ofthe chest, then the clutch is disengaged. The belt encoder is used bythe control system to track the take-up of the belt, and to limit thelength of belt which is spooled upon the drive belt.

As illustrated in these embodiments, the drive spool has a smalldiameter such that several rotations of the drive spool are possible(and generally necessary) to effect resuscitative compression. The drivespool diameter is preferably in the range of 0.5 to 2.5 cm. Thus,rotation of a 2.5 cm diameter spool through 1.5 revolution will berequired to effect a nominal change in belt length of 12 cm, androtation of a 0.5 cm diameter spool through eight revolutions will berequired to effect a nominal change in belt length of 12 cm. Themultiple rotations of the spool help limit motor overrun after detectionof a system feedback or physiologic feedback parameter and subsequentsystem response in stopping the motor, engaging the brake, disengagingthe clutch, etc. so that a small motor overrun will result in a smallerbelt overrun. The optimal size of the shaft, and all the shafts in thesystem, will vary with the choice of other components, and the angularencoders used in the system may be calibrated according to theparticular geometry effective at the shaft to which they are attached.

In order to control the amount of thoracic compression (change incircumference) for the cardiac compression device using the encoder, thecontrol system must establish a baseline or zero point for belt take-up.When the belt is tight to the point where any slack has been taken up,the motor will require more current to continue to turn under the loadof compressing the chest. This, the expected rapid increase in motorcurrent draw (motor threshold current draw), is measured through atorque sensor (an Amp meter, a voltage divider circuit or the like).This spike in current or voltage is taken as the signal that the belthas been drawn tightly upon the patient and the paid out belt length isan appropriate starting point. The encoder measurement at this point iszeroed within the system (that is, taken as the starting point for belttake-up). The encoder then provides information used by the system todetermine the change in length of the belt from this pre-tightened or“pre-tensioned” position. The ability to monitor and control the changein length allows the controller to control the amount of pressureexerted on the patient and the change in volume of the patient bylimiting the length of belt take-up during a compression cycle. To aidin the identification of the pre-tensioned belt position, the voltageapplied to the motor may be limited during the pre-tensioning, therebyslowing the motor, increasing the torque of the motor, and leading tothe higher, more easily recognized current spike or current increaseupon meeting the resistance of the body. As alternatives to analyzingmotor current or torque applied at some point in the system to determinethe pre-tensioned position, the rate of belt take up can be monitoredthrough the position encoders illustrated in the several embodiments,either reading the length of deployed or spooled belt from the beltencoder or reading the position of one of the rotating components (whichwill be related to belt length by a simple multiple). During slack takeup, the rate of belt length change (Δl/Δt) may be monitored and analyzedfor abrupt changes or a decrease below a certain rate, which will varywith the particular drive train used.

The expected length of belt take-up for optimum compression is 1 to 6inches. However, six inches of travel on a thin individual may create aexcessive change in thoracic circumference and present the risk ofinjury from the device. In order to overcome this problem, the systemdetermines the necessary change in belt length required by measuring orusing the amount of belt travel required to become taut. Knowing theinitial length of the belt and subtracting off the amount required tobecome taut will provide a measure of the patient's size (chestcircumference). The system then relies on predetermined limits orthresholds to the allowable change in circumference for each patient onwhich it is installed, which can be used to limit the change in volumeand pressure applied to the patient. The threshold may change with theinitial circumference of the patient so that a smaller patient willreceive less of a change in circumference as compared to a largerpatient (or vice versa, should experience prove that optimal compressionextent of compression is inversely related to chest size). The encoderprovides constant feedback as to the state of travel and thus thecircumference of the patient at any given time. When the belt take-upreaches the threshold (change in volume), the system controller ends thecompression stroke and continues into the next period of hold or releaseas required by the compression/decompression regimen programmed into thecontroller. The encoder also enables the system to limit the release ofthe belt so that it does not fully release. This release point can bedetermined by the zero point established on the pre-tightening firsttake-up, or by taking a percentage of the initial circumference or asliding scale triggered by the initial circumference of the patient.

The belt could also be buckled so that it remains tight against thepatient. Requiring the operator to tighten the belt provides for amethod to determine the initial circumference of the patient. Againencoders can determine the amount of belt travel and thus can be used tomonitor and limit the amount of change in the circumference of thepatient given the initial circumference.

Several compression and release patterns may be employed to boost theeffectiveness of the CPR compression. Typical CPR compression isaccomplished at 60 to 80 cycles per minute, with the cycles constitutingmere compression followed by complete release of compressive force. Thisis the case for manual CPR as well as for known mechanical and pneumaticchest compression devices. With our new system, compression cycles inthe range of 20 to 70 cpm have been effective, and the system may beoperated as high as 120 cpm or more, This type of compression cycle canbe accomplished with the motor box with motor and clutch operation asindicated in FIG. 28. When the system is operating in accordance withthe timing table of FIG. 28, the motor is always on, and the clutchcycles between engagement (on) and release (off). After severalcompressions at time periods T1, T3, T5 and T7, the system pauses forseveral time periods to allow a brief period (several seconds) toprovide a respiration pause, during which operators may provideventilation or artificial respiration to the patient, or otherwise causeoxygenated air to flow into the patient's lungs. (The brakes illustratedin FIG. 25, are not used in this embodiment, though they may beinstalled.) The length of the clutch engagement period is controlled inthe range of 0 to 2000 msec, and the time between periods of clutchengagement is controlled in the range of 0 to 2000 msec (which, ofcourse, is dictated by medical considerations and may change as more islearned about the optimal rate of compression).

The timing chart of FIG. 28a illustrates the intrathoracic pressurechanges caused by the compression belt when operated according to thetiming diagram of FIG. 28. The chest compression is indicated by thestatus line 119. The motor is always on, as indicated by motor statusline 120. The clutch is engaged or “on” according to the square waveclutch status line 121 in the lower portion of the diagram. Each timethe clutch engages, the belt is tightened around the patient's chest,resulting in a high pressure spike in belt tension and intrathoracicpressure as indicated by the compression status line 119. Pulses p1, p2,p3, p4 and p5 are all similar in amplitude and duration, with theexception of pulse p3. Pulse p3 is limited in duration in this exampleto show how the torque limit feedback operates to prevent excessive beltcompression. (Torque limit may be replaced by belt travel or otherparameter as the limiting parameter.) As an example of system responseto sensing the torque limit, Pulse p3 is shown rapidly reaching thetorque limit set on the motor. When the torque limit is reached, theclutch disengages to prevent injury to the patient and excessive drainon the battery (excessive compression is unlikely to lead to additionalblood flow, but will certainly drain the batteries quickly). Note thatafter clutch disengagement under pulse p3, belt tension andintra-thoracic pressure drop quickly, and the intra-thoracic pressure isincreased for only a small portion of cycle. After clutch disengagementbased on an over-torque condition, the system returns to the pattern ofrepeated compressions. Pulse p4 occurs at the next scheduled compressionperiod T7, after which the respiration pause period spanning T8, T9, andT10 is created by maintaining the clutch in the disengaged condition.After the respiration pause, pulse p5 represents the start of the nextset of compressions. The system repeatedly performs sets of compressionsfollowed by respiration pauses until interrupted by the operator.

FIG. 29 illustrates the timing of the motor, clutch and cam brake in asystem that allows the belt compression to be reversed by reversing themotor. It also provides for compression hold periods to enhance thehemodynamic effect of the compression periods, and relaxation holds tolimit the belt pay-out in the relaxation period to the point where thebelt is still taut on the chest and not excessively loose. As thediagram indicates, the motor operates first in the forward direction totighten the compression belt, then it is turned off for a brief period,then operates in the reverse direction and turns off, and continues tooperate through cycles of forward, off, reverse, off, and so on. Inparallel with these cycles of the motor state, the cam brake isoperating to lock the motor shaft in place, thereby locking the drivespool in place and preventing movement of the compression belt. Brakestatus line 122 indicates the status of the brake 105. Thus, when themotor tightens the compression belt up to the threshold or time limit,the motor turns off and the cam brake engages to prevent the compressionbelt from loosening. This effectively prevents relaxation of thepatient's chest, maintaining a higher intrathoracic pressure during holdperiods T2, T6 and T10. Before the next compression cycle begins, themotor is reversed and the cam brake is disengaged, allowing the systemto drive the belt to a looser length and allowing the patient's chest torelax. Upon relaxation to the lower threshold corresponding to thepre-tightened belt length, the cam brake is energized to stop the spooland hold the belt at the pretightened length. The clutch is engaged atall times (the clutch may be omitted altogether if no other compressionregimen is desired in the system). (This embodiment may incorporate twomotors operating in different directions, connecting to the spoolthrough clutches.)

FIG. 29a illustrates the intrathoracic pressure changes caused by thecompression belt when operated according to the timing diagram of FIG.29. The clutch, if any, is always on as indicated by clutch status line121. The cam brake is engaged or “on” according to the brake status line122, which includes the square wave in the lower portion of the diagram.The motor is on, off, or reversed according to motor state line 120.Each time the motor is turned on in the forward direction, the belt istightened around the patient's chest, resulting in a high pressure spikein belt tension and intrathoracic pressure as shown in the pressure plotline 119. Each time the high threshold limit is sensed by the system,the motor is de-energized, and the cam brake engages to prevent furtherbelt movement. This results in a high maintained pressure or “holdpressure” during the hold periods indicated on the diagram (time periodT2, for example). At the end of the hold period, the motor is reversedto drive the belt to a relaxed position, then de-energized. When themotor is turned off after a period of reverse operation, the cam brakeengages to prevent excess slacking of the compression belt, which wouldwaste time and battery power. The cam brake disengages when the cycle isreinitiated and the motor is energized to start another compression.Pulses p1, p2, are similar in amplitude and duration. Pulse p3 islimited in duration in this example to show how the torque limitfeedback operates to prevent excessive belt compression. Pulse p3rapidly reaches the torque limit set on the motor (or the take-up limitset on the belt), and the motor stops and the cam brake engages toprevent injury to the patient and excessive drain on the battery. Notethat after motor stop and cam brake engagement under pulse p3, belttension and intra-thoracic pressure are maintained for the same periodas all other pulses, and the intra-thoracic pressure is decreased onlyslightly, if at all, during the high pressure hold period. After pulse,p3, a respiration pause may be initiated in which the belt tension ispermitted to go completely slack.

FIG. 30 illustrates the timing of the motor, clutch and cam brake in asystem that allows the belt compression to completely relax during eachcycle. As the table indicates, the motor operates only in the forwarddirection to tighten the compression belt, then is turned off for abrief period, and continues to operate through on and off cycles. In thefirst time period T1, the motor is on and the clutch is engaged,tightening the compression belt about the patient. In the next timeperiod T2, the motor is turned off and the cam brake is energized (withthe clutch still engaged) to lock the compression belt in the tightenedposition. In the next time period T3, the clutch is disengaged to allowthe belt to relax and expand with the natural relaxation of thepatient's chest. In the next period T4, the motor is energized to comeup to speed, while the clutch is disengaged and the cam brake is off.The motor comes up to speed with no effect on the compression belt inthis time period. In the next time period, the cycle repeats itself.Thus, when the motor tightens the compression belt up to the thresholdor time limit, the motor turns off and the cam brake engages to preventthe compression belt from loosening. This effectively preventsrelaxation of the patient's chest, maintaining a higher intrathoracicpressure. Before the next compression cycle begins, the clutch isdisengaged, allowing the chest to relax and allowing the motor to comeup to speed before coming under load. This provides much more rapid beltcompression, leading to a sharper increase in intrathoracic pressure.

FIG. 30a illustrates the intrathoracic pressure changes caused by thecompression belt when operated according to the timing table of FIG. 30.The clutch is turned on only after the motor has come up to speed,according to the clutch status line 121 and motor status line 120, whichshows that the motor is energized for two time periods before clutchengagement. The cam brake is engaged or “on” according to the brakestatus line 122 in the lower portion of the diagram. Each time theclutch is engaged, the belt is tightened around the patient's chest,resulting in a sharply increasing high pressure spike in belt tensionand intrathoracic pressure as shown in the pressure plot line 119. Eachtime the motor is de-energized, the cam brake engages and clutch remainsengaged to prevent further belt movement, and the clutch preventsrelaxation. This results in a high maintained pressure or “holdpressure” during the hold periods indicated on the diagram. At the endof the hold period, the clutch is de-energized to allow the belt toexpand to the relaxed position. At the end of the cycle, the cam brakeis disengaged (with the clutch disengaged) to allow the motor to come upto speed before initiation of the next compression cycle. The next cycleis initiated when the clutch is engaged. This action produces thesharper pressure increase at the beginning of each cycle, as indicatedby the steep curve at the start of each of the pressure Pulses p1, p2,and p3. Again, these pressure pulses are all similar in amplitude andduration, with the exception of pulse p2. Pulse p2 is limited induration in this example to show how the torque limit feedback operatesto prevent excessive belt compression. Pulse p2 rapidly reaches thetorque limit set on the motor, and the motor stops and the cam brakeengages to prevent injury to the patient and excessive drain on thebattery. Note that after motor stop and cam brake engagement under pulsep2, belt tension and intra-thoracic pressure are maintained for the sameperiod as all other pulses, and the intrathoracic pressure is decreasedonly slightly during the hold period. The operation of the systemaccording to FIG. 30a is controlled to limit belt pressure to athreshold measured by high motor torque (or, correspondingly, beltstrain or belt length).

FIG. 31 illustrates the timing of the motor, clutch and cam brake in asystem that does not allow the belt compression to completely relaxduring each cycle. Instead, the system limits belt relaxation to a lowthreshold of motor torque, belt strain, or belt length. As the tableindicates, the motor operates only in the forward direction to tightenthe compression belt, then is turned off for a brief period, andcontinues to operate through on and off cycles. In the first time periodT1, the motor is on and the clutch is engaged, tightening thecompression belt about the patient. In the next time period T2, themotor is turned off and the cam brake is energized (with the clutchstill engaged) to lock the compression belt in the tightened position.In the next time period T3, the clutch is disengaged to allow the beltto relax and expand with the natural relaxation of the patient's chest.The drive spool will rotate to pay out the length of belt necessary toaccommodate relaxation of the patient's chest. In the next period T4,while the motor is still off, the clutch is engaged (with the cam brakestill on) to prevent the belt from becoming completely slack. To startthe next cycle at T5, the motor starts and the cam brake is turned offand another compression cycle begins.

FIG. 31a illustrates the intrathoracic pressure and belt strain thatcorresponds to the operation of the system according to FIG. 31. Motorstatus line 120 and the brake status line 122 indicate that when themotor tightens the compression belt up to the high torque threshold ortime limit, the motor turns off and the cam brake engages to prevent thecompression belt from loosening. Thus the high pressure attained duringuptake of the belt is maintained during the hold period starting at T2.When the belt is loosened at T3 by release of the clutch (whichuncouples the cam brake), the intrathoracic pressure drops as indicatedby the pressure line 119. At T4, after the compression belt has loosenedto some degree, but not become totally slack, the clutch engages (andre-couples the cam brake) to hold the belt at some minimum level of beltpressure. This effectively prevents total relaxation of the patient'schest, maintaining a slightly elevated intrathoracic pressure evenbetween compression cycles. A period of low level compression is createdwithin the cycle. Note that after several cycles (four or five cycles) arespiration pause is incorporated into the compression pattern, duringwhich the clutch is off, the cam brake is off to allow for completerelaxation of the belt and the patient's chest. (The system may beoperated with the low threshold in effect, and no upper threshold ineffect, creating a single low threshold system.) The motor may beenergized between compression period, as shown in time periods T11 andT12, to bring it up to speed before the start of the next compressioncycle.

FIG. 32 shows a timing table for use in combination with a system thatuses the motor, clutch, and secondary brake 113 or a brake on drivewheel or the drive spool itself. The brake 105 is not used in thisembodiment of the system (though it may be installed in the motor box).As the motor status line 120 indicates, the motor operates only in theforward direction to tighten the compression belt, and is always on. Inthe first time period T1, the motor is on and the clutch is engaged,tightening the compression belt about the patient. In the next timeperiod T2, the motor is on but the clutch is disengaged and the brake isenergized to lock the compression belt in the tightened position. In thenext time period T3, the clutch is disengaged and the brake is off toallow the belt to relax and expand with the natural relaxation of thepatient's chest. The drive spool will rotate to pay out the length ofbelt necessary to accommodate relaxation of the patient's chest. In thenext period T4, while the motor is still on, the clutch is disengaged,but energizing the secondary brake is effective to lock the belt preventthe belt from becoming completely slack (in contrast to the systemsdescribed above, the operation of the secondary brake is effective whenthe clutch is disengaged because the secondary brake is downstream ofthe clutch). To start the next cycle at T5, the motor starts and thesecondary brake is turned off, the clutch is engaged and anothercompression cycle begins. During pulse p3, the clutch is engaged fortime periods T11 and T12 while the torque threshold limit is notachieved by the system. This provides an overshoot compression period,which can be interposed amongst the torque limited compression periods.

FIG. 32a illustrates the intrathoracic pressure and belt strain thatcorrespond to the operation of the system according to FIG. 32. Motorstatus line 120 and the brake status line 122 indicate that when themotor tightens the compression belt up to the high torque threshold ortime limit, the secondary brake engages (according to secondary brakestatus line 122) and the clutch disengages to prevent the compressionbelt from loosening. Thus the high pressure attained during uptake ofthe belt is maintained during the hold period starting at T2. When thebelt is loosened at T3 by release of the secondary brake, theintrathoracic pressure drops as indicated by the pressure line. At T4,after the compression belt has loosened to some degree, but not becometotally slack, the secondary brake engages to hold the belt at someminimum level of belt pressure. This effectively prevents totalrelaxation of the patient's chest, maintaining a slightly elevatedintrathoracic pressure even between compression cycles. A period of lowlevel compression is created within the cycle. At P3, the upperthreshold is not achieved but the maximum time allowed for compressionis reached, so and the clutch is engaged for two time periods T9 and T10until the system releases the clutch based on the time limit. At T9 andT10, the secondary brake, though enabled, is not turned on.

FIG. 33 shows a timing table for use in combination with a system thatuses the motor, clutch, and secondary brake 113 or a brake on drivewheel or the drive spool itself. The brake 105 is not used in thisembodiment of the system (though it may be installed in the motor box).As the motor status line 120 indicates, the motor operates only in theforward direction to tighten the compression belt, and is always on. Inthe time periods T1 and T2, the motor is on and the clutch is engaged,tightening the compression belt about the patient. In contrast to thetiming chart of FIG. 32, the brake is not energized to hold the beltduring the compression periods (T1 and T2) unless the upper threshold isachieved by the system. In the next time period T3, the clutch isdisengaged and the brake is off to allow the belt to relax and expandwith the natural relaxation of the patient's chest. The drive spool willrotate to pay out the length of belt necessary to accommodate relaxationof the patient's chest. During T3, the belt pays out to the zero point,so the system energizes the secondary brake. During T4, the motorremains on, the clutch is disengaged, and the secondary brake iseffective to lock the belt to prevent the belt from becoming completelyslack (in contrast to the systems using the cam brake, the operation ofthe secondary brake is effective when the clutch is disengaged becausethe secondary brake is downstream of the clutch). To start the nextcycle at T5, the motor continues and the secondary brake is turned off,the clutch is engaged and another compression cycle begins. The systemachieves the high threshold during time period T6, at peak p2, andcauses the clutch to release and the secondary brake to engage, therebyholding the belt tight in the high compression state for the remainderof the compression period (T5 and T6). At the end of the compressionperiod, the brake is momentarily disengaged to allow the belt to expandto the low threshold or zero point, and the brake is engaged again tohold the belt at the low threshold point. Pulse p3 is created withanother compression period in which brake is released and the clutch isengaged in T9 and T10, until the threshold is reached, whereupon theclutch disengages and the brake engages to finish the compression periodwith the belt held in the high compression state. In time periods T11and T12, the clutch is disengaged and the brake is released to allow thechest to relax completely. This provides for a respiration pause inwhich the patient may be ventilated.

FIG. 33a illustrates the intrathoracic pressure and belt strain thatcorresponds to the operation of the system according to FIG. 33. In timeperiods T1 and T2, the motor status line 120 and the secondary brakestatus line 122 indicate that the motor tightens the compression belt upto the end of the compression period (the system will not initiate ahold below the upper threshold). When the belt is loosened at T3 byrelease of the secondary brake, the intrathoracic pressure drops asindicated by the pressure line. At T3, after the compression belt hasloosened to some degree, but not become totally slack, the secondarybrake engages to hold the belt at some minimum level of belt pressure.This effectively prevents total relaxation of the patient's chest,maintaining a slightly elevated intrathoracic pressure even betweencompression cycles. A period of low level compression is created withinthe cycle. Motor status line 120 and the brake status line 122 indicatethat when the motor tightens the compression belt up to the high torquethreshold or time limit, the secondary brake engages and the clutchdisengages to prevent the compression belt from loosening. Thus the highpressure attained during uptake of the belt is maintained during thehold period starting at T6. When the belt is loosened at T7 by releaseof the secondary brake, the intrathoracic pressure drops as indicated bythe pressure line. At T7, after the compression belt has loosened tosome degree, but not become totally slack, the secondary brake engagesto hold the belt at the lower threshold. At p3, the upper threshold isagain achieved, so and the clutch is disengaged and the brake is engagedat time T10 to initiate the high compression hold.

FIG. 34 shows a timing table for use in combination with a system thatuses the motor, clutch, and secondary brake 113 or a brake on drivewheel or the drive spool itself. The brake 105 is not used in thisembodiment of the system (though it may be installed in the motor box).As the motor status line 120 indicates, the motor operates only in theforward direction to tighten the compression belt, and is always on. Inthe first time period T1, the motor is on and the clutch is engaged,tightening the compression belt about the patient. In the next timeperiod T2, the motor is on, the clutch is disengaged in response to thesensed threshold, and the brake 113 is enabled and energized to lock thecompression belt in the tightened position only if the upper thresholdis sensed during the compression period. In the next time period T3, theclutch is disengaged and the brake is off to allow the belt to relax andexpand with the natural relaxation of the patient's chest. The drivespool will rotate to pay out the length of belt necessary to accommodaterelaxation of the patient's chest. In the next period T4, while themotor is still on, the clutch is disengaged, but energizing thesecondary brake is effective to lock the belt preventing the belt frombecoming completely slack (in contrast to the systems described above,the operation of the secondary brake is effective when the clutch isdisengaged because the secondary brake is downstream of the clutch). Tostart the next cycle at T5, the motor continues running and thesecondary brake is turned off, the clutch is engaged and anothercompression cycle begins. During pulse p3, the clutch is on in timeperiod T9. The clutch remains engaged and the brake is enabled but notenergized in time period T10. The clutch and brake are controlled inresponse to the threshold, meaning that the system controller is waitinguntil the high threshold is sensed before switching the system to thehold configuration in which the clutch is released and the brake isenergized. In this example, the high threshold is not achieved duringcompression periods T9 and T10, so the system does not initiate a hold.

FIG. 34a illustrates the intrathoracic pressure and belt strain thatcorrespond to the operation of the system according to FIG. 34. Motorstatus line 120 and the secondary brake status line 122 indicate thatwhen the motor tightens the compression belt up to the high torquethreshold or time limit, the clutch disengages and the secondary brakeengages to prevent the compression belt from loosening. Thus the highpressure attained during uptake of the belt is maintained during thehold period starting at T2. The period of compression comprises a periodof active compressing of the chest followed by a period of staticcompression. When the belt is loosened at T3 by release of the secondarybrake, the intrathoracic pressure drops as indicated by the pressureline 119. At T4, after the compression belt has loosened to some degree,but not become totally slack, the secondary brake engages to hold thebelt at some minimum level of belt pressure. This effectively preventstotal relaxation of the patient's chest maintaining a slightly elevatedintrathoracic pressure between compression cycles. A period of low levelcompression is created within the cycle. Note that in cycles where theupper threshold is not achieved, the compression period does not includea static compression (hold) period, and the clutch is engaged for twotime periods T9 and T10, and the system eventually ends the activecompression based on the time limit set by the system.

FIG. 35 shows a timing table for use in combination with a system thatuses the motor, clutch, the cam brake 105 and a secondary brake 113 (ora brake on drive wheel or the spindle itself). Both brakes are used inthis embodiment of the system. As the table indicates, the motoroperates only in the forward direction to tighten the compression belt.In the first time period T1, the motor is on and the clutch is engaged,tightening the compression belt about the patient. In the next timeperiod T2, the upper threshold is achieved and the motor is turned offin response to the sensed threshold, the clutch is still engaged, andthe cam brake is enabled and energized to lock the compression belt inthe tightened position (these events happen only if the upper thresholdis sensed during the compression period). In the next time period T3,with the clutch disengaged and the brakes off, the belt relaxes andexpands with the natural relaxation of the patient's chest. The drivespool will rotate to pay out the length of belt necessary to accommodaterelaxation of the patient's chest. In the next period T4 (while themotor is still on), the clutch remains disengaged, but energizing thesecondary brake is effective to lock the belt to prevent the belt frombecoming completely slack. To start the next cycle at T5, the secondarybrake is turned off, the clutch is engaged and another compression cyclebegins (the motor has been energized earlier, in time period T3 or T4,to bring it up to speed). During pulse p3, the clutch is on in timeperiod T9. The clutch remains engaged and the cam brake is enabled butnot energized in time period T10. The clutch and cam brake arecontrolled in response to the threshold, meaning that the systemcontroller is waiting until the high threshold is sensed beforeswitching the system to the hold configuration in which the clutch isreleased and the cam brake is energized. In this example, the highthreshold is not achieved during the compression periods T9 and T10, sothe system does not initiate a hold. The cam brake serves to hold thebelt in the upper threshold length, and the secondary brake serves tohold the belt in the lower threshold length.

FIG. 35a illustrates the intrathoracic pressure and belt strain thatcorresponds to the operation of the system according to FIG. 35. Motorstatus line 120 and the cam brake status line 122 indicate that when themotor tightens the compression belt up to the high torque threshold ortime limit, the motor turns off and the cam brake engages to prevent thecompression belt from loosening (the clutch remains engaged). Thus thehigh pressure attained during uptake of the belt is maintained duringthe hold period starting at T2. Thus the period of compression comprisesa period of active compressing of the chest followed by a period ofstatic compression. When the belt is loosened at T3 by release of theclutch, the intrathoracic pressure drops as indicated by the pressureline 119. At T4, after the compression belt has loosened to some degree,but not become totally slack, the secondary brake engages to hold thebelt at some minimum level of belt pressure, as indicated by thesecondary brake status line 123. This effectively prevents totalrelaxation of the patient's chest, maintaining a slightly elevatedintrathoracic pressure even between compression cycles. A period of lowlevel compression is created within the cycle. Note that in cycles wherethe upper threshold is not achieved, the compression period does notinclude a static compression (hold) period, and the clutch is engagedfor two time periods T9 and T10, and the system eventually ends theactive compression based on the time limit set by the system.

The previous figures have illustrated control systems in a time dominantsystem, even where thresholds are used to limit the active compressionstroke. We expect the time dominant system will be preferred to ensure aconsistent number of compression periods per minute, as is currentlypreferred in the ACLS. Time dominance also eliminates the chance of arunaway system, where the might be awaiting indication that a torque orencoder threshold has been met, yet for some reason the system does notapproach the threshold. However, it may be advantageous in some systems,perhaps with patients closely attended by medical personnel, to allowthe thresholds to dominate partially or completely. An example ofpartial threshold dominance is indicated in the table of FIG. 36. Thecompression period is not timed, and ends only when the upper thresholdis sensed at point A. The system operates the clutch and brake to allowrelaxation to the lower threshold at point B, and then initiates the lowthreshold hold period. At a set time after the peak compression, a newcompression stroke is initiated at point C, and maintained until thepeak compression is reached at point D. The actual time spent in theactive compression varies depending on how long it takes the system toachieve the threshold. Thus cycle time (a complete period of activecompression, release and low threshold hold, until the start of the nextcompression) varies with each cycle depending on how long it takes thesystem to achieve the threshold, and the low threshold relaxation periodfloats accordingly. To avoid extended periods in which the system stallswhile awaiting an upper threshold that is never achieved, an outer timelimit is imposed on each compression period, as illustrated at point G,where the compression is ended before reaching the maximum allowedcompression. In essence, the system clock is reset each time the upperthreshold is achieved. The preset time limits 135 for low compressionhold periods are shifted leftward on the diagram of FIG. 36a, tofloating time limits 136. This approach can be combined with each of theprevious control regimens by resetting the timing whenever those systemsreach the upper threshold.

The arrangement of the motor, cam brake and clutch may be applied toother systems for belt driven chest compressions. For example, Lach,Resuscitation Method And Apparatus, U.S. Pat. No. 4,770,164 (Sep. 13,1988) proposes a hand-cranked belt that fits over the chest and twochocks under the patient's chest. The chocks hold the chest in placewhile the belt is cranked tight. Torque and belt tightness are limitedby a mechanical stop which interferes with the rotation of the largedrive roller. The mechanical stop merely limits the tightening roll ofthe spool, and cannot interfere with the unwinding of the spool. A motoris proposed for attachment to the drive rod, and the mate between themotor shaft and the drive roller is a manually operated mechanicalinterlock referred to as a clutch. This “clutch” is a primitive clutchthat must be set by hand before use and cannot be operated duringcompression cycles. It cannot release the drive roller during a cycle,and it cannot be engaged while the motor is running, or while the deviceis in operation. Thus application of the brake and clutch arrangementsdescribed above to a device such as Lach will be necessary to allow thatsystem to be automated, and to accomplish the squeeze and holdcompression pattern.

Lach, Chest Compression Apparatus for Cardiac Arrest, PCT App.PCT/US96/18882 (Jun. 26, 1997) also proposes a compression belt operatedby a scissor-like lever system, and proposes driving that system with amotor which reciprocatingly drives the scissor mechanism back and forthto tighten and loosen the belt. Specifically, Lach teaches that failureof full release is detrimental and suggests that one cycle ofcompression would not start until full release has occurred. This systemcan also be improved by the application of the clutch and brake systemsdescribed above. It appears that these and other belt tensioning meanscan be improved upon by the brake and clutch system. Lach discloses anumber of reciprocating actuators for driving the belt, and requiresapplication of force to these actuators. For example, the scissormechanism is operated by applying downward force on the handles of thescissor mechanism, and this downward force is converted into belttightening force by the actuator. By motorizing this operation, theadvantages of our clutch and brake system can be obtained with each ofthe force converters disclosed in Lach. The socketed connection betweenthe motor and drive spool can be replaced with a flexible drive shaftconnected to any force converter disclosed in Lach.

FIG. 37 illustrates an embodiment of the chest compression device with asternal bladder. The compression belt 3 incorporates an air bladder 140which, in use, is located on the inner side of the compression vest overthe sternum of the patient, and may be of various sizes with a volume ofjust a few cubic centimeters of air to several hundred cubic centimetersof air, up to about one liter. The compression belt in this case issecured to the body with two overlapping areas 141R and 141L of hook andloop fastener (Velcro®) or other fastener, with the air bladderpreferably located over the sternum of the patient. During compression,the bladder itself is also compressed by the belt, and this compressioncauses an increase in the pressure in the air bladder. A pressure sensoroperably connected through a sensing line 142 to the air bladder 140senses the pressure in the air bladder and transmits a correspondingsignal to the controller. Since a sensing line is used, the pressuretransducer may be located off the belt and may be placed inside thecontrol box, and the sensing line must then reach from the bladder(under the belt) to the control box. (The pressure sensor may instead belocated within the bladder itself, requiring an electrical power andsignal transmission cable 143 extending from the bladder to the controlbox.) The pressure bladder is preferably located on the length of belton the same side of the patient as the control system (in this case, theleft side belt segment 64L) so that the sensing line or electrical cabledoes not interfere with placement of the belt on the patient. Thepressure bladder may be located anywhere on the belt, such as below thepatient's spine, but as described below placement over the sternum helpscontrol the compressed shape of the thorax. (Several bladders may bedistributed around the thorax to indicate local pressure around thecircumference of the thorax. For example, bladders may be located on thelateral surface of the chest, between the chest and the compressionbelt, in parasaggital locations on the front of the chest, between thechest and the compression belt, and in parasaggital locations betweenthe back and the compression belt (or backboard). With several bladdersplaced around the chest and connected to pressure transducers, the forceprofile on an test subject or actual patient may be recorded andcompared to blood flow, so that the effect of varying the force profilecan be determined.)

The controller may incorporate the pressure signal into its controlalgorithm by limiting the take-up of the belt so as not to exceed200-300 mmHg in the air bladder (since the pressure in the air bladdershould correspond directly to the pressure exerted on the patientschest) (240 mmHg is currently preferred). The pressure signal may alsobe used to ensure that pressure in the air bladder, and correspondinglypressure exerted on the patient, reaches a minimum effective pressure ofabout 240 mmHG in each compression. The air bladder is filled with avolume of air prior to use, and need not be further inflated duringstorage or use unless it is prone to leakage. The pressure signal mayalso be used as an indication that the belt has been pre-tensioned, andall slack had been taken up, whereupon the controller can record anencoder reading which is used as the starting point for determining theamount of belt movement that has occurred during a given compression.Currently, pressure of 10 to 50 mmHg in the bladder is used as thepre-tensioned point. While air is our preferred fluid, the bladder mayfilled with any fluid, gel or other medium capable of transmittingpressure to a pressure sensor, and will operate to provide a pressuresensing volume and/or a shape control volume. When filled with air, thebladder will be slightly compressible and have a variable volume, andwhen filled with fluid such as water, the bladder will be incompressibleand have an essentially fixed volume. Alternate means for sensingpressure or force applied to the body may be used, including pressuretransducers, force transducers and force sensing resistors mounted onthe belt between the belt and the patient.

FIG. 38 illustrates an embodiment of the chest compression belt withsingle layer pull straps connecting the belt to the drive spool. Thebelt is comprised as in previous embodiments with left and right beltportions 64L and 64R and the fastening ends 92L and 92R which are fittedwith hook and loop fastening elements 95. The belt left and right beltportions 64L and 64R in this embodiment are joined to two pull straps144, and may be joined directly to the two pull straps or joinedindirectly by intermediate segments of straps 145 and 146. The spool end147 of the pull straps connects to the drive spool. Each pull strapoperates equally on each of the left and right belt segments,eliminating the torque effect of spooling the belt over itself asdescribed in reference to FIGS. 16 through 22.

FIG. 40 illustrates another embodiment of the chest compression beltwith single layer pull straps connecting the belt to the drive spool. Inthis embodiment, the left and right belt portions 64L and 64R of thebelt are fixed together at the lower ends corresponding to the spine ofthe patient, and secured to the straps 144. The lower ends (the endsthat join with the pull straps) 148 of each belt portion may be fixedtogether with stitching, adhesives or other methods. The upper ends 149(the ends that mate over the sternum) of the belts portions are providedwith hook and loop fastener pads.

The spool end of the pull straps may be attached to the drive spool asillustrated in FIG. 41. The pull straps 144 are secured to the spinalarea of the belt by stitching, adhesives, or other method. The spoolends 147 of each pull strap are provided with a set of several grommetsor eyelets 200 and 201 for attachment to the matching sets of pins 202and 203 countersunk in the drive spool 68. As illustrated, the pins areset in the floor of strap receiving recesses 204 and 205. At least oneof the pins in each set is an internally or externally threaded pin (206and 207) capable of receiving a threaded bolt or screw over it. Therecess caps 208 and 209 are placed over the strap ends after they areengaged with the posts to secure them in place. The caps may be screwedonto the drive spool and over the strap ends with a screw or internallythreaded screws 210 and 211 screwed onto the threaded pins. With thisarrangement, installation and replacement of belts is facilitated, anddrive spool manufacture is simplified.

The pull straps may be replaced with a single broad segment of the beltwhich is joined together such that their can be no differential in thespooling of the left and right belt sections upon rotation of the spool.This is illustrated in FIG. 39, where belt 64 is a plain band ofmaterial with fastening ends 92L and 92R, corresponding left and rightbelt portions 64L and 64R, a spool engaging center portion 93. In thisembodiment, the left belt and right belt portions of the belt in thespool engaging center portion are stitched together to prevent slidingof one side over the other in the spooling length of the belt, thuspreventing uneven take-up of the belt resulting from the differentcircumferential travel of one side over the other side while spooling onthe spool. Thus, FIG. 39 illustrates an embodiment of the chestcompression belt with non-torquing spooling segment connecting the beltto the drive spool.

FIG. 42 illustrates an embodiment of the chest compression device with aspinal support plate 150. The compression belt left section 64L andright sections 64R are joined in a seam 151 to pull straps 144 as shownin FIG. 38, and the pull straps are fixed to the drive spool 68 withinthe cartridge 63. The compression belt right section 64R extends fromthe pull strap medial end 152 (that is, the end near the medial area ofthe body, when applied to a patient), under the medially located lowerspindle 153 and the slightly lateral upper right spindle 154, under thespinal support platform 150 and further outward to extend under theright flank of the patient when in use. The compression belt leftsection 64L extends from the pull strap medial end 152 (that is, the endnear the medial area of the body, when applied to a patient), reversingdirection around the slightly lateral upper left spindle 155, under thespinal support platform 150 and further outward to extend under the leftflank of the patient when in use. The spinal support platform 150extends inferiorly and superiorly (upward and downward) over thecartridge, and serves to support the patient over the cartridge and awayfrom the underlying area in which the belt runs into the cartridge, thuseliminating a large portion of the frictional load which the belt wouldotherwise have to overcome during operation. The PTFE sheet 72 may beprovided on the upper surface of the spinal support platform to reducefriction and rubbing due to chest compression.

FIGS. 43 and 44 illustrate the operation of the compression device whenfitted with the features described in FIGS. 37 through 39. As shown inFIG. 43, the compression belt 64 is wrapped around the patient's thorax80. The bladder 140 is placed between the patient and the left beltportion 64L over the patient's sternum 82 because the motor box andcontrol box are located on the left side of the patient. In this crosssection of the device, the connection of the belt to the pull straps isillustrated, with the pull straps 144 connected at their medial end 152to the left and right belt portions, and connected at their spool end147 to the drive spool 68 (it can appreciated in this view that thecompression belt may be made of a single length of belt, with the pullstraps being secured at its midsection, or may be made of two separatelengths of belt secured at their respective medial ends to the pullstraps). The connection of the pull straps to the drive spool, ratherthan direct connection of the belt midsection to the drive spool,results in a uniform pull length (as illustrated in FIG. 44) on eachside of the belt, which eliminates the torque on the body resulting fromthe extra pull length created when spooling two layers of strap or beltover one another, as described in reference to FIGS. 16 and 17. As withprevious embodiments, the drive spool rotates through severalrevolutions, taking up several layers of pull straps, to accomplish thebelt tightening in each compression cycle.

Also shown in FIGS. 43 and 44 is the effect of the fixed bladder on theshape of the thorax after compression. During compression of the patientwith the bladder installed between the patient and the belt, the thoraxis maintained in a somewhat oval cross section, and is preferentiallycompressed in the front to back direction (arrow 156). We also refer tothis form of compression as anterior-posterior compression or sternalcompression, in contrast to the circumferential compression describedearlier. The shape of the compressed torso is urged toward a flat ovoidshape, and away from the rounder, more circular shape of the torso whichresults without the bladder as shown in FIG. 45 (some patients, forunknown reasons, tend to compress more readily from the sides, resultingin the rounder shape in the cross section of the torso). Using thebladder avoids the tendency in some patients to compress into a roundercross section compressed excessively in the lateral dimension direction(line 157), thus potentially lifting the sternum upwardly. Thus, thephysical presence of the bladder, whether or not used for feedbackcontrol, is advantageous in the operation of the device. The roundedshape compressions, while useful, are believed to have lower efficiencyin terms of the correlation between compression of the chest andcompression of the heart and thoracic aorta.

The operation of the spinal support platform 150 can also be seen inFIGS. 43 and 44. The platform extends laterally across the spinaldepression 158 which runs up and down the back. The width of the spinalsupport platform is chosen so that, in most patients, it extendslaterally to the shoulder blades (scapula) 159 or medial border of thescapula 160 of the patient, or to the protrusion of the trapezius muscle161 on either side of the spinal depression of the back (area 158). Theplatform thus spans the spinal depression, and extends bi-laterallyacross the spinal depression to the protrusions of the trapezius muscleor the medial border of the shoulder blade. The belt sections 64R and64L pass under the platform through a vertical gap 163 between theplatform and the cartridge or backplate, thereby avoiding runningdirectly between the patient's body and the cartridge for a smalllateral width extending slightly beyond the width of the platform.

FIG. 46 is modification of the device shown in FIG. 42. In this crosssection of the chest compression device, the guide spindles 153 (centerspindle), 154 (right spindle) and 155 (left spindle) are laterallyspaced from each other to alter the force profile of the compressionbelt. The left and right guide spindles are located farther toward thesides of the patient in this device than they are in FIG. 42, where theyare essentially located under the spine. Here, the guide spindles arelocated several inches laterally of the spine, and lie under the scapulaor trapezius region of the patient. This location alters the forceprofile of the belt, creating a generally anterior to posterior force onthe thorax, rather than a circumferentially uniform force profile. Theexact location of the guide spindles may be adjusted either furtherlaterally, or medially (back toward the center position immediatelyunder the spine, as in FIG. 42) to increase or decrease the balancebetween anterior to posterior force and circumferential force applied tothe typical patient. The addition of lateral support plates 164 and 165on the right and left sides of the body provide support for the patient,and also form, with the spinal support plate 150, the gaps through whichthe belt passes to extend from the cartridge to the patient.

In the embodiment of FIG. 46, sternal displacement is closely related tothe spool rotations. Using a spool having a 0.5 inch diameter, and usinga light Tyvek® fabric or similar material, with a material thickness ofabout 0.020 inches, sternal displacement is can be theoreticallycalculated by the formula:

Apdisplacement=(0.0314(rev.)²+1.5394(rev.))−(0.0314(take-uprev.)²+1.5394(take-up rev.))

Alternatively, observation of sternal displacement versus spoolrotations leads empirically to the formula:

APdisplacement(empirical)=(0.0739(rev.)²+1.4389(rev.))−(0.0739(take-uprev.)²+1.4389(take-up rev.)).

In these equations, (rev.) is the total number of revolutions of thespool, as measured by an encoder in the system capable of measuringspool rotations, either directly or indirectly; (take-up rev.) is thenumber of revolutions required to take up any slack in the belt,according to the methods described above. Either of these equations maybe used by the controller of the system to calculate the amount ofdisplacement, either as a back-up to other feed back control methods oras a primary method. In both equations, the controller software keepstrack of the take-up revolutions, and the otherwise expected sternaldisplacement from these revolutions is subtracted from the displacementcalculated from the total number of revolutions to provided the actualsternal displacement from a given number of rotations after take-up ofslack. The displacement information can be used by the system to informthe system as to the patient's initial height, which can then becorrelated to a desired sternal displacement (big people need morecompression). Currently, sternal compression of 1 to 2 inches or twentypercent of sternal height is desired. Either of these sternaldisplacement goals may be met by calculating the sternal displacement asindicated above. Additionally, from the initial take-up, anapproximation may be made as to the size of the patient, and thisinformation may be used to determined the desired sternal displacement,and/or adjust other thresholds of the system if desired. For example,knowing the initial length of the entire belt, and subtracting thelength spooled during take-up, the length of belt deployed about thepatient can be calculated.

FIG. 47 shows embodiments of the motor box 62 and the coupling betweenthe motor 103 and the drive spool 68. The drive spool and motor areagain aligned in a folded, anti-parallel relationship, so that the motorlies laterally outside the drive spool relative to the patient when inuse. The motor output shaft 104 drives reduction gears 168, and thereduction gear output shaft 169 drives a non-reversing coupling 170, andthe output shaft 171 of the non-reversing coupling drives the sprocketedoutput wheel 112. The sprocketed output wheel 112 in turn drives thechain 172 and the sprocketed drive wheel 66 and the drive spool. Anon-reversing coupling 170 is interposed in the drive train, for exampleat the output of the reduction gear (as shown) or at the output of thedrive spool sprocket. The non-reversing coupling may be driven in eitherclockwise or counterclockwise direction when the input shaft is turnedby the drive train inputs upstream from the coupling, so that rotationof the input shaft 169 is possible, and results in rotation of theoutput shaft 171. However, rotation of the output shaft, driven from thedownstream side of the drive train (as might occur during chestexpansion) is prohibited by internal mechanisms of the coupling, andthus does not reverse power the input shaft.

Several different types of such non-reversing couplings may be used, andare referred to as bi-directional no-back couplings or bi-directionalreverse locking couplings. For example, the bi-directional no-backcouplings available from Warner Electric incorporates wrap-down springsand interfering tangs. The coupling can be turned only when torque isapplied to the input shaft, which may be driven in either direction, butwhen there is no torque on the input, the output shaft is effectivelylocked and cannot be rotated in either direction. Any torque applied tothe output shaft is transmitted to the clutch body, and will not betransmitted to the input shaft. The bi-directional no-back couplingsavailable from Formsprag Engineering incorporate sprags within theclutch body which interfere with reversing rotation of the output shaft.

The bi-directional no-back coupling installed in the drive train may beused instead of the clutches and brakes described in relation to FIG.25. In operation, the braking and clutching action is replaced by thereverse locking function of the coupling. As shown in FIG. 48, thetiming of the system operation is greatly simplified. During eachcompression stroke, the motor is operated in the tightening directionuntil the desired feedback limit is reached. The motor is then stopped.The upper level hold is achieved automatically by the reverse lockingbehavior of the coupling. At the end of the hold period, the motor isoperated in reverse, in the loosening direction, whereupon the couplingautomatically unlocks and permits loosening rotation. If a lowerthreshold hold period is desired, the motor is stopped, whereuponcontinued loosening rotation of the drive spool is prohibited by thereverse-locking behavior of the coupling. The motor may be stopped inthe loosening direction in response to feedback based on belt length(from the belt encoders), the pressure in the air bladder, torque on themotor, or other feedback indicating that the low threshold belt positionhas been reached. Ventilation pauses in which the belt is completelyloosened may be interposed between sets of compressions by driving themotor in the loosening direction well past the low threshold. The finalposition of the belt in the ventilation pause may be determined by fromthe encoders, from the pressure in the bladder, or other feedback.

FIG. 48 illustrates the intrathoracic pressure and belt strain thatcorresponds to the operation of the system which uses a non-reversingcoupling. Motor status line 120 and the non-reversing coupling line 173indicate that when the motor is operating to tighten the compressionbelt up to the high torque threshold or time limit, the non-reversingcoupling is driven by the motor. When the motor turns off, thenon-reversing coupling locks to prevent the compression belt fromloosening. The coupling locks to prevent reversing without any inputfrom the controller. Thus the high pressure attained during uptake ofthe belt is maintained during the hold period starting at T2. When thebelt is loosened at T3 by operating the motor in reverse or looseningdirection, with inherent release of the internal locking mechanisms ofthe non-reversing coupling, and the intrathoracic pressure drops asindicated by the compression status line 119. At T4, after thecompression belt has loosened to some degree, but not become totallyslack, the motor is stopped, and the non-reversing coupling locks (againwithout any input or control signal from the controller) to hold thebelt at some minimum level of belt pressure. This effectively preventstotal relaxation of the patient's chest, maintaining a slightly elevatedintra thoracic pressure even between compression cycles. A period of lowlevel compression is created within the cycle. Note that after severalcycles (four or five cycles) a respiration pause is incorporated intothe compression pattern, for which the motor is driven in reverse toloosen the belt for complete relaxation of the belt and the patient'schest. As with previously described embodiments of the motor box andcontroller, the system may be operated with the low threshold in effect,and no upper threshold in effect, or with an upper threshold in effectwith no lower threshold in effect. It will be noted in the descriptionthat reverse operation of the motor refers to operation of the motor inthe loosening operation, as compared to forward operation which refersto operation of the motor in the tightening direction. In contrast, whenspeaking of the non-reversing coupling, reversing refers toreverse-powering the coupling by turning the output shaft to causerotation of the input shaft. Thus, although the non-reversing couplingwill not allow reverse powering, it can rotate in the forward andreverse, clockwise or counterclockwise, and loosening or tighteningdirections, as those terms are used in reference to the motor.

Thus far, we have described the use of pressure feedback control, beltlength or volume feedback control, and motor torque control. It appearsfrom our experience that pressure and thoracic volume are related insuch a manner that compression cycles may be controlled with feedbackregarding the relationship between the measured volume and the sensedpressure. Thus, the control of the motor, clutch, brake and othercomponents of the drive train may be controlled as a function of therelationship between the force applied to the body and change in thelength of the belt. The pressure applied to the thorax is measured, asindicated above, by measuring the pressure in the air bladderillustrated in FIG. 37, or with pressure transducers, force transducersor other means for sensing force applied to the body Torque sensorsoperably connected to the belt through by connection at any point in thedrive train or by sensing motor current, may also be used to sense theforce applied to the body The length is measured by scanning the beltencoder or scanning rotary encoders in the drive train, as describedabove (any other mechanism for measuring belt length may be used). Thevolume is computed using belt length as a proxy for circumference of thechest, and assuming a circular cross section of the chest. The change involume is computed based on an 20 cm wide belt and assuming a chest witha circular cross section, and the volume encompassed by the belt isequal to the belt length times the belt width, so that the change involume is computed as Δv=Δ (cross section)×20 cm. The change in beltlength is measures through an encoder placed in one of several places inthe system as described above.

FIG. 49 illustrates the relationship between the change in thoracicvolume compression (or change in belt length) versus the thoracicpressure. As illustrated in the graph, an initial large negative changein volume Δv₁ (large increments of compression) causes a small change inthoracic pressure Δp₁, while the same volume change Δv₂ near the end ofthe compression results in a large increase in pressure Δp₂. Conversely,large changes in pressure are required to produce small changes involume at the end of the compression. This is an asymptotic curve with aslope approaching zero. When little or no volume change results from anincremental change in pressure, further efforts by the system tocompress the chest are wasteful of battery power, and can be avoided.Thus, the control system is programmed to monitor inputs correspondingto thoracic volume (deployed belt length or other proxy) and thoracicpressure (bladder pressure or other proxy), and limit motor operation byending a compression when the ratio of volume change versus pressurechange (the slope of the curve in FIG. 49) falls below a preset value.Currently, the preset value is experimentally determined to be in therange of 0.05 to 0.5 cm²/mmhg. Correspondingly, if belt length is usedas the basis for calculation, the control system is programmed tomonitor inputs corresponding to deployed belt length and thoracicpressure (bladder pressure or other proxy), and limit motor operation byending a compression when the ratio of belt length change versuspressure change (the slope of the curve in FIG. 49 falls below a presetvalue.

FIG. 50 illustrates the relationship between the slope of the curve inFIG. 49 and the actual pressure in the bladder. The slope of the curvein FIG. 49 is charted as a function of the actual pressure in bladder.As indicated by the graph, the slope of the curve Δp/Δv approaches zerowhen pressure approaches 300 mmHg in the bladder. This is the valueexpected for humans; in animal studies the slope approaches zero atabout 300 mmHg. The controller for the system can operate to limit motoroperation by ending a compression when the value or slope of this curveapproaches a preset value (close to zero). Currently, the preset valueis experimentally determined to be in the range of 0.05 to 0.15mm²/mmHg². This value will be reached at different pressures for eachpatient, and at different pressures during the course of treatment of asingle patient. It often is reached when pressure is well below 300 mmHgin the air bladder. In regards to both the slope of the curve v(p) ofFIG. 49 (that is, the change in volume as a function of the change inpressure) and the slope or value of the curve Δv/Δp(p) in FIG. 50 (thatis, the ratio of an incremental change in volume to the incrementalchange in pressure in the bladder as a function of pressure in thebladder; the incremental change may also be referred to as thederivative of the functions of volume and pressure versus time), theoptimum value for all patients falls within a narrow range as comparedto the actual pressure required for adequate compression.

Operation of the system in response to the dual parameters of pressureand volume, and factoring in the rate of change of these parametersprovides an unforeseen advantage to the operation of the system. Theoptimum change in volume, considered alone, or the optimum change inpressure, considered alone, may vary within a substantial range frompatient to patient. This requires that volume and pressure changes mustbe excessive for some patients to ensure that they are sufficient forall patients (even considering the great advantage of using torquefeedback and torque limits, which optimizes the amount of force appliedwhile minimizing the draw on the battery). However, it appears fromempirical studies that Δv/ΔAp(p) curve varies only slightly from patientto patient. This allows control of the system within narrow ranges ofΔv/Δp, and minimizes the waste of battery power required when the systemis operated in response to less uniform parameters. Thus, operation inresponse to reaching the threshold illustrated in FIG. 49 is desirablesince it applies to all patients with little variation.

Operation in response to reaching the threshold illustrated in FIG. 50is desirable for the same reason, and also eliminates reliance on theactual values of the parameters. In this manner the controller isprogrammed to operate the motor to tighten the belt about the chest ofthe patient until the signal corresponding to pressure in the bladderindicates that optimal resuscitative compression of the patient's chesthas been achieved. The optimal resuscitative compression in this case isexpressed as the degree of compression that achieves a first ratio ofchange in volume over change in pressure in the range of −0.05 to −0.5,or achieves a second ratio of this first ratio over the actual pressurein the bladder in the range of −0.05 to −0.15. While this method hasbeen discussed in terms of volume of the chest, the volume isapproximated as a product of the belt length, and belt length may byused instead of chest volume in the computations. It should be notedthat the actual length of the belt at any point need not be known, asthe computations described above consider the change in belt length.

FIGS. 51 and 52 illustrate additional embodiments of the motor and drivetrain used to drive the drive spool. In these embodiments, a clutch neednot be used, and the brake is located off-line relative to the drivetrain, and is connected to the drive train through a take-off. The motor103 drives the motor shaft 104, gearbox output rotor 106 and sprocketedoutput wheel 107 through the gearbox 180. The output wheel 107 driveschain 108 which in turn rotates the drive sprocket wheel 181 and spooldrive wheel 66. The drive spool 68 is operably connected to the drivewheel with the receiving rod which fits into a socket in the drivewheel. Interposed between the drive sprocket and the drive wheel is atorque sensor 182 which senses actual torque on the drive spool andtransmits a corresponding signal to the controller. Interposed betweenthe gearbox and the output wheel 107 is an additional sprocket wheel183, which is connected via brake chain 184 to brake sprocket wheel 185mounted on brake shaft 186 to the brake 187. The brake is anelectromechanical brake operable by the controller. The various sprocketwheels are chosen in sizes to effect desired gear reduction and gearingchanges. The motor used in our preferred embodiment rotates at about15,000 rpm. The gearbox reduces the rotation to about 2,100 rpm (a 7:1reduction), and the sprockets 107 and 181 are sized to effect a 2:1reduction, so that the spool rotates at about 1,000 rpm. The brakingsprockets 183 and 185 sized to effect a 1:2 reduction, so that the brakeshaft 186 rotates at about 4,200 rpm. In other embodiments, the motorrotates at about 10,000 rpm; the gearbox reduces the rotation to about1,000 rpm (a 10:1 reduction), and the sprockets 107 and 181 are sized toeffect a 3:1 reduction, so that the spool rotates at about 333 rpm; thebraking sprockets 183 and 185 sized to effect a 1:3 reduction, so thatthe brake shaft 186 rotates at about 3,000 rpm.

FIG. 52 shows another arrangement for installation of an off-line brake.As in FIG. 51, the motor 103 drives the motor shaft 104, gearbox outputrotor 106, and sprocketed output wheel 107 through the gearbox 180. Theoutput wheel 107 drives chain 108 which in turn rotates the drivesprocket 181 and spool drive wheel 66. The drive spool 68 is operablyconnected to the drive wheel. In this embodiment, the brake 187 isconnected to the drive spool 68 via spool mounted brake shaft 186 andbrake sprocket 185 mounted on this brake shaft. The brake chain 184 andbrake sprocket 190 connects the brake to the drive spool. As indicatedin phantom, the brake can be connected to the drive spool at either endof the drive spool, with the brake connected to brake shaft 186,extending from the drive sprocket 181 and brake sprocket 189. Thisenables connection of both the drive and the brake on the motor box sideof the drive spool, retaining the potential for a modular system inwhich the drive spool (and the remainder of the compression beltcartridge) can easily be removed from the drive wheel and remainder ofthe motor box. The brake is connected through a take-off on the drivespool in FIG. 52, whereas it is connected to the drive train through atake-off on the gearbox output shaft in FIG. 51. By connecting the braketo a take-off, rather than in line as illustrated in FIG. 25, forexample, the gearing of the brake may be adjusted, thereby reducing thetorque requirements on the brake, and allowing use of a smaller andlighter brake, and allowing much faster braking than an in-line brake.Also, any after braking motion is reduced in effect at the spool by thevarious gearing changes, thus serving to limit belt overrun after thesystem operates the brake.

Belt overrun, which we use to refer to the condition in which the beltcontinues to tighten after the controller has operated to end acompression, wastes battery power and exerts more force on the patientthan is desired. Also, slight delays or lag in the apparent bladderpressure (force applied to the body) causes overshoot in the systemoperation, so that even if system response were instantaneous, pressurein excess of the predetermined thresholds might be applied duringroutine operation. To limit these problems, the control system may beprogrammed to test the device and calibrate the system setpoints withthe desired thresholds. This is illustrated in FIG. 53, whichillustrates the actual and setpoint pressures for a series ofcompressions performed by the system for calibration purposes.

As shown in FIG. 53, in compression 1, the system selects a relativelylow set-point, for example 140 mmHg in the bladder. By the time thesystem senses 140 mmHg in the bladder and stops compression, bladderpressure overshoots the setpoint substantially. The control systemcompares this actual pressure to its predetermined threshold of desiredpressure on the patient of, for example, 240 mmHg, and determines thatthe overshoot is insufficient to meet the threshold, so the setpoint of140 mmHg is insufficient to use as a setpoint. In the next compression,the control system selects a slightly higher setpoint of 160 mmHg,compresses to that setpoint, and observes the overshoot in the actualpressure reach about 200 mmHg, and determines that the overshoot isinsufficient to meet the threshold, so the setpoint of 140 mmHg isinsufficient to use as a setpoint. The control system continues testingin this manner until it observes, in a compression such as compression 5in the chart, that a set-point of 220 mmHg leads to an overshoot to thedesired threshold of 240 mmHg, and then selects 220 mmHg as a setpointto be used by the system to achieve the desired threshold of 240 mmHg insubsequent compressions.

During the course of CPR, the overshoot may vary for numerous reasons,including changing elasticity of the patient's chest, temperature of thebladder, etc. The system continues to compare the actual pressure withthe setpoint pressure, and adjusts accordingly. For example, incompression n in the chart, the actual pressure does not reach thethreshold of 240 mmHg, so the system raises the setpoint slightly incompression n+1 and thereafter. Conversely, if the system observes thatthe actual pressure exceeds the threshold, the setpoint is lowered untilactual pressure registers at the threshold. In this manner, the batteryused to power the system is not consumed by the application of wastedpressure on the patient, but is not wasted by conservative andunproductive application of force below the threshold.

Many embodiments of CPR devices and control methods have been describedabove. While the preferred embodiments of the devices and methods havebeen described in reference to the environment in which they weredeveloped, they are merely illustrative of the principles of theinventions. Other embodiments and configurations may be devised withoutdeparting from the spirit of the inventions and the scope of theappended claims.

We claim:
 1. A device for compressing the chest of a patient comprising:a belt adapted to extend around the chest of the patient and fastened onthe patient; a drive spool operably connected to the belt for repeatedlytightening and loosening the belt around the chest of the patient; amotor operably connected to the drive spool through a drive train, saidmotor capable of operating the drive spool repeatedly to cause the beltto tighten about the chest of the patient and loosen about the chest ofthe patient; said drive train comprising a motor shaft, a gearbox with agearbox output shaft, a first sprocket wheel mounted on the gearboxoutput shaft, said first sprocket wheel being connected to a secondsprocket wheel mounted on the drive spool through a first chain; a brakehaving a brake shaft, and a third sprocket wheel mounted therein, saidthird sprocket wheel being connected to a fourth sprocket wheel througha second chain, said fourth sprocket wheel being connected to the drivespool; and a controller for controlling operation of the motor andbrake, said controller programmed to operate the motor and brake tocause repeated cycles of tightening and loosening of the belt, andintermittently operating the brake to hold the belt at a threshold oftightness.
 2. The device of claim 1 wherein the third sprocket wheel andfourth sprocket wheel are sized relative to each other to effect agearing change which increases the speed of the brake shaft relative tothe drive spool.
 3. The device of claim 2 where the first sprocket wheeland second sprocket wheel are sized relative to each other to effect agearing change which decreases the speed of the drive spool relative tothe gearbox output shaft.
 4. A device for compressing the chest of apatient comprising: a belt adapted to extend at least partially aroundthe chest of the patient; a drive spool operably connected to the beltfor repeatedly tightening and loosening the belt around the chest of thepatient; a brake having a brake shaft, said brake operably connected tothe drive spool and capable of holding the drive spool in a tightenedstate about the chest of the patient; a motor operably connected to thedrive spool through a drive train, said motor capable of operating thedrive spool repeatedly to cause the belt to tighten about the chest ofthe patient and loosen about the chest of the patient; said drive traincomprising a motor shaft, a gearbox with a gearbox output shaft, a firstsprocket wheel mounted on the gearbox output shaft and a second sprocketwheel mounted on the gearbox output shaft; said brake being connected tothe first sprocket wheel through a first chain, said first chainconnected to a third sprocket wheel which is connected to the brakeshaft; said drive spool being connected to the second sprocket wheelthrough a second chain, said second chain connected to a fourth sprocketwheel which is connected to the drive spool; a controller forcontrolling operation of the motor and brake, said controller programmedto operate the motor and brake to cause repeated cycles of tighteningand loosening of the belt, and intermittently operating the brake tohold the belt at a threshold of tightness.
 5. The device of claim 4wherein the first sprocket wheel and third sprocket wheel are sizedrelative to each other to effect a gearing change which increases thespeed of the brake shaft relative to the gearbox output shaft.
 6. Thedevice of claim 5 where the second sprocket wheel and fourth sprocketwheel are sized relative to each other to effect a gearing change whichdecreases the speed of the drive spool relative to the gearbox outputshaft.